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Java example source code file (OGLContext.c)

This example Java source code file (OGLContext.c) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

check_previous_op, gl_false, gl_true, gl_zero, j2drlstraceln, j2dtraceln, jni_false, jni_true, null, oglcontext_createfragmentprogram, oglcontext_isextensionavailable, oglcontext_isfbobjectextensionavailable, oglsdops, return_if_null

The OGLContext.c Java example source code

/*
 * Copyright (c) 2004, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

#ifndef HEADLESS

#include <stdlib.h>
#include <string.h>

#include "sun_java2d_SunGraphics2D.h"

#include "jlong.h"
#include "jni_util.h"
#include "OGLContext.h"
#include "OGLRenderQueue.h"
#include "OGLSurfaceData.h"
#include "GraphicsPrimitiveMgr.h"
#include "Region.h"

/**
 * The following methods are implemented in the windowing system (i.e. GLX
 * and WGL) source files.
 */
extern jboolean OGLSD_InitOGLWindow(JNIEnv *env, OGLSDOps *oglsdo);
extern OGLContext *OGLSD_MakeOGLContextCurrent(JNIEnv *env,
                                               OGLSDOps *srcOps,
                                               OGLSDOps *dstOps);

/**
 * This table contains the standard blending rules (or Porter-Duff compositing
 * factors) used in glBlendFunc(), indexed by the rule constants from the
 * AlphaComposite class.
 */
OGLBlendRule StdBlendRules[] = {
    { GL_ZERO,                GL_ZERO                }, /* 0 - Nothing      */
    { GL_ZERO,                GL_ZERO                }, /* 1 - RULE_Clear   */
    { GL_ONE,                 GL_ZERO                }, /* 2 - RULE_Src     */
    { GL_ONE,                 GL_ONE_MINUS_SRC_ALPHA }, /* 3 - RULE_SrcOver */
    { GL_ONE_MINUS_DST_ALPHA, GL_ONE                 }, /* 4 - RULE_DstOver */
    { GL_DST_ALPHA,           GL_ZERO                }, /* 5 - RULE_SrcIn   */
    { GL_ZERO,                GL_SRC_ALPHA           }, /* 6 - RULE_DstIn   */
    { GL_ONE_MINUS_DST_ALPHA, GL_ZERO                }, /* 7 - RULE_SrcOut  */
    { GL_ZERO,                GL_ONE_MINUS_SRC_ALPHA }, /* 8 - RULE_DstOut  */
    { GL_ZERO,                GL_ONE                 }, /* 9 - RULE_Dst     */
    { GL_DST_ALPHA,           GL_ONE_MINUS_SRC_ALPHA }, /*10 - RULE_SrcAtop */
    { GL_ONE_MINUS_DST_ALPHA, GL_SRC_ALPHA           }, /*11 - RULE_DstAtop */
    { GL_ONE_MINUS_DST_ALPHA, GL_ONE_MINUS_SRC_ALPHA }, /*12 - RULE_AlphaXor*/
};

/** Evaluates to "front" or "back", depending on the value of buf. */
#define OGLC_ACTIVE_BUFFER_NAME(buf) \
    (buf == GL_FRONT || buf == GL_COLOR_ATTACHMENT0_EXT) ? "front" : "back"

/**
 * Initializes the viewport and projection matrix, effectively positioning
 * the origin at the top-left corner of the surface.  This allows Java 2D
 * coordinates to be passed directly to OpenGL, which is typically based on
 * a bottom-right coordinate system.  This method also sets the appropriate
 * read and draw buffers.
 */
static void
OGLContext_SetViewport(OGLSDOps *srcOps, OGLSDOps *dstOps)
{
    jint width = dstOps->width;
    jint height = dstOps->height;

    J2dTraceLn4(J2D_TRACE_INFO,
                "OGLContext_SetViewport: w=%d h=%d read=%s draw=%s",
                width, height,
                OGLC_ACTIVE_BUFFER_NAME(srcOps->activeBuffer),
                OGLC_ACTIVE_BUFFER_NAME(dstOps->activeBuffer));

    // set the viewport and projection matrix
    j2d_glViewport(dstOps->xOffset, dstOps->yOffset,
                   (GLsizei)width, (GLsizei)height);
    j2d_glMatrixMode(GL_PROJECTION);
    j2d_glLoadIdentity();
    j2d_glOrtho(0.0, (GLdouble)width, (GLdouble)height, 0.0, -1.0, 1.0);

    // set the active read and draw buffers
    j2d_glReadBuffer(srcOps->activeBuffer);
    j2d_glDrawBuffer(dstOps->activeBuffer);

    // set the color mask to enable alpha channel only when necessary
    j2d_glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, (GLboolean)!dstOps->isOpaque);
}

/**
 * Initializes the alpha channel of the current surface so that it contains
 * fully opaque alpha values.
 */
static void
OGLContext_InitAlphaChannel()
{
    GLboolean scissorEnabled;

    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_InitAlphaChannel");

    // it is possible for the scissor test to be enabled at this point;
    // if it is, disable it temporarily since it can affect the glClear() op
    scissorEnabled = j2d_glIsEnabled(GL_SCISSOR_TEST);
    if (scissorEnabled) {
        j2d_glDisable(GL_SCISSOR_TEST);
    }

    // set the color mask so that we only affect the alpha channel
    j2d_glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_TRUE);

    // clear the color buffer so that the alpha channel is fully opaque
    j2d_glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    j2d_glClear(GL_COLOR_BUFFER_BIT);

    // restore the color mask (as it was set in OGLContext_SetViewport())
    j2d_glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_FALSE);

    // re-enable scissor test, only if it was enabled earlier
    if (scissorEnabled) {
        j2d_glEnable(GL_SCISSOR_TEST);
    }
}

/**
 * Fetches the OGLContext associated with the given destination surface,
 * makes the context current for those surfaces, updates the destination
 * viewport, and then returns a pointer to the OGLContext.
 */
OGLContext *
OGLContext_SetSurfaces(JNIEnv *env, jlong pSrc, jlong pDst)
{
    OGLSDOps *srcOps = (OGLSDOps *)jlong_to_ptr(pSrc);
    OGLSDOps *dstOps = (OGLSDOps *)jlong_to_ptr(pDst);
    OGLContext *oglc = NULL;

    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_SetSurfaces");

    if (srcOps == NULL || dstOps == NULL) {
        J2dRlsTraceLn(J2D_TRACE_ERROR,
            "OGLContext_SetSurfaces: ops are null");
        return NULL;
    }

    J2dTraceLn2(J2D_TRACE_VERBOSE, "  srctype=%d dsttype=%d",
                srcOps->drawableType, dstOps->drawableType);

    if (dstOps->drawableType == OGLSD_TEXTURE) {
        J2dRlsTraceLn(J2D_TRACE_ERROR,
            "OGLContext_SetSurfaces: texture cannot be used as destination");
        return NULL;
    }

    if (dstOps->drawableType == OGLSD_UNDEFINED) {
        // initialize the surface as an OGLSD_WINDOW
        if (!OGLSD_InitOGLWindow(env, dstOps)) {
            J2dRlsTraceLn(J2D_TRACE_ERROR,
                "OGLContext_SetSurfaces: could not init OGL window");
            return NULL;
        }
    }

    // make the context current
    oglc = OGLSD_MakeOGLContextCurrent(env, srcOps, dstOps);
    if (oglc == NULL) {
        J2dRlsTraceLn(J2D_TRACE_ERROR,
            "OGLContext_SetSurfaces: could not make context current");
        return NULL;
    }

    // update the viewport
    OGLContext_SetViewport(srcOps, dstOps);

    // perform additional one-time initialization, if necessary
    if (dstOps->needsInit) {
        if (dstOps->isOpaque) {
            // in this case we are treating the destination as opaque, but
            // to do so, first we need to ensure that the alpha channel
            // is filled with fully opaque values (see 6319663)
            OGLContext_InitAlphaChannel();
        }
        dstOps->needsInit = JNI_FALSE;
    }

    return oglc;
}

/**
 * Resets the current clip state (disables both scissor and depth tests).
 */
void
OGLContext_ResetClip(OGLContext *oglc)
{
    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_ResetClip");

    RETURN_IF_NULL(oglc);
    CHECK_PREVIOUS_OP(OGL_STATE_CHANGE);

    j2d_glDisable(GL_SCISSOR_TEST);
    j2d_glDisable(GL_DEPTH_TEST);
}

/**
 * Sets the OpenGL scissor bounds to the provided rectangular clip bounds.
 */
void
OGLContext_SetRectClip(OGLContext *oglc, OGLSDOps *dstOps,
                       jint x1, jint y1, jint x2, jint y2)
{
    jint width = x2 - x1;
    jint height = y2 - y1;

    J2dTraceLn4(J2D_TRACE_INFO,
                "OGLContext_SetRectClip: x=%d y=%d w=%d h=%d",
                x1, y1, width, height);

    RETURN_IF_NULL(dstOps);
    RETURN_IF_NULL(oglc);
    CHECK_PREVIOUS_OP(OGL_STATE_CHANGE);

    if ((width < 0) || (height < 0)) {
        // use an empty scissor rectangle when the region is empty
        width = 0;
        height = 0;
    }

    j2d_glDisable(GL_DEPTH_TEST);
    j2d_glEnable(GL_SCISSOR_TEST);

    // the scissor rectangle is specified using the lower-left
    // origin of the clip region (in the framebuffer's coordinate
    // space), so we must account for the x/y offsets of the
    // destination surface
    j2d_glScissor(dstOps->xOffset + x1,
                  dstOps->yOffset + dstOps->height - (y1 + height),
                  width, height);
}

/**
 * Sets up a complex (shape) clip using the OpenGL depth buffer.  This
 * method prepares the depth buffer so that the clip Region spans can
 * be "rendered" into it.  The depth buffer is first cleared, then the
 * depth func is setup so that when we render the clip spans,
 * nothing is rendered into the color buffer, but for each pixel that would
 * be rendered, a non-zero value is placed into that location in the depth
 * buffer.  With depth test enabled, pixels will only be rendered into the
 * color buffer if the corresponding value at that (x,y) location in the
 * depth buffer differs from the incoming depth value.
 */
void
OGLContext_BeginShapeClip(OGLContext *oglc)
{
    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_BeginShapeClip");

    RETURN_IF_NULL(oglc);
    RESET_PREVIOUS_OP();

    j2d_glDisable(GL_SCISSOR_TEST);

    // enable depth test and clear depth buffer so that depth values are at
    // their maximum; also set the depth func to GL_ALWAYS so that the
    // depth values of the clip spans are forced into the depth buffer
    j2d_glEnable(GL_DEPTH_TEST);
    j2d_glClearDepth(1.0);
    j2d_glClear(GL_DEPTH_BUFFER_BIT);
    j2d_glDepthFunc(GL_ALWAYS);

    // disable writes into the color buffer while we set up the clip
    j2d_glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);

    // save current transform
    j2d_glMatrixMode(GL_MODELVIEW);
    j2d_glPushMatrix();

    // use identity transform plus slight translation in the z-axis when
    // setting the clip spans; this will push the clip spans (which would
    // normally be at z=0) to the z=1 plane to give them some depth
    j2d_glLoadIdentity();
    j2d_glTranslatef(0.0f, 0.0f, 1.0f);
}

/**
 * Finishes setting up the shape clip by resetting the depth func
 * so that future rendering operations will once again be written into the
 * color buffer (while respecting the clip set up in the depth buffer).
 */
void
OGLContext_EndShapeClip(OGLContext *oglc, OGLSDOps *dstOps)
{
    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_EndShapeClip");

    RETURN_IF_NULL(dstOps);
    RETURN_IF_NULL(oglc);
    RESET_PREVIOUS_OP();

    // restore transform
    j2d_glPopMatrix();

    // re-enable writes into the color buffer
    j2d_glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, (GLboolean)!dstOps->isOpaque);

    // enable the depth test so that only fragments within the clip region
    // (i.e. those fragments whose z-values are >= the values currently
    // stored in the depth buffer) are rendered
    j2d_glDepthFunc(GL_GEQUAL);
}

/**
 * Initializes the OpenGL state responsible for applying extra alpha.  This
 * step is only necessary for any operation that uses glDrawPixels() or
 * glCopyPixels() with a non-1.0f extra alpha value.  Since the source is
 * always premultiplied, we apply the extra alpha value to both alpha and
 * color components using GL_*_SCALE.
 */
void
OGLContext_SetExtraAlpha(jfloat ea)
{
    J2dTraceLn1(J2D_TRACE_INFO, "OGLContext_SetExtraAlpha: ea=%f", ea);

    j2d_glPixelTransferf(GL_ALPHA_SCALE, ea);
    j2d_glPixelTransferf(GL_RED_SCALE, ea);
    j2d_glPixelTransferf(GL_GREEN_SCALE, ea);
    j2d_glPixelTransferf(GL_BLUE_SCALE, ea);
}

/**
 * Resets all OpenGL compositing state (disables blending and logic
 * operations).
 */
void
OGLContext_ResetComposite(OGLContext *oglc)
{
    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_ResetComposite");

    RETURN_IF_NULL(oglc);
    CHECK_PREVIOUS_OP(OGL_STATE_CHANGE);

    // disable blending and XOR mode
    if (oglc->compState == sun_java2d_SunGraphics2D_COMP_ALPHA) {
        j2d_glDisable(GL_BLEND);
    } else if (oglc->compState == sun_java2d_SunGraphics2D_COMP_XOR) {
        j2d_glDisable(GL_COLOR_LOGIC_OP);
        j2d_glDisable(GL_ALPHA_TEST);
    }

    // set state to default values
    oglc->compState = sun_java2d_SunGraphics2D_COMP_ISCOPY;
    oglc->extraAlpha = 1.0f;
}

/**
 * Initializes the OpenGL blending state.  XOR mode is disabled and the
 * appropriate blend functions are setup based on the AlphaComposite rule
 * constant.
 */
void
OGLContext_SetAlphaComposite(OGLContext *oglc,
                             jint rule, jfloat extraAlpha, jint flags)
{
    J2dTraceLn1(J2D_TRACE_INFO,
                "OGLContext_SetAlphaComposite: flags=%d", flags);

    RETURN_IF_NULL(oglc);
    CHECK_PREVIOUS_OP(OGL_STATE_CHANGE);

    // disable XOR mode
    if (oglc->compState == sun_java2d_SunGraphics2D_COMP_XOR) {
        j2d_glDisable(GL_COLOR_LOGIC_OP);
        j2d_glDisable(GL_ALPHA_TEST);
    }

    // we can safely disable blending when:
    //   - comp is SrcNoEa or SrcOverNoEa, and
    //   - the source is opaque
    // (turning off blending can have a large positive impact on
    // performance)
    if ((rule == RULE_Src || rule == RULE_SrcOver) &&
        (extraAlpha == 1.0f) &&
        (flags & OGLC_SRC_IS_OPAQUE))
    {
        J2dTraceLn1(J2D_TRACE_VERBOSE,
                    "  disabling alpha comp: rule=%d ea=1.0 src=opq", rule);
        j2d_glDisable(GL_BLEND);
    } else {
        J2dTraceLn2(J2D_TRACE_VERBOSE,
                    "  enabling alpha comp: rule=%d ea=%f", rule, extraAlpha);
        j2d_glEnable(GL_BLEND);
        j2d_glBlendFunc(StdBlendRules[rule].src, StdBlendRules[rule].dst);
    }

    // update state
    oglc->compState = sun_java2d_SunGraphics2D_COMP_ALPHA;
    oglc->extraAlpha = extraAlpha;
}

/**
 * Initializes the OpenGL logic op state to XOR mode.  Blending is disabled
 * before enabling logic op mode.  The XOR pixel value will be applied
 * later in the OGLContext_SetColor() method.
 */
void
OGLContext_SetXorComposite(OGLContext *oglc, jint xorPixel)
{
    J2dTraceLn1(J2D_TRACE_INFO,
                "OGLContext_SetXorComposite: xorPixel=%08x", xorPixel);

    RETURN_IF_NULL(oglc);
    CHECK_PREVIOUS_OP(OGL_STATE_CHANGE);

    // disable blending mode
    if (oglc->compState == sun_java2d_SunGraphics2D_COMP_ALPHA) {
        j2d_glDisable(GL_BLEND);
    }

    // enable XOR mode
    j2d_glEnable(GL_COLOR_LOGIC_OP);
    j2d_glLogicOp(GL_XOR);

    // set up the alpha test so that we discard transparent fragments (this
    // is primarily useful for rendering text in XOR mode)
    j2d_glEnable(GL_ALPHA_TEST);
    j2d_glAlphaFunc(GL_NOTEQUAL, 0.0f);

    // update state
    oglc->compState = sun_java2d_SunGraphics2D_COMP_XOR;
    oglc->xorPixel = xorPixel;
    oglc->extraAlpha = 1.0f;
}

/**
 * Resets the OpenGL transform state back to the identity matrix.
 */
void
OGLContext_ResetTransform(OGLContext *oglc)
{
    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_ResetTransform");

    RETURN_IF_NULL(oglc);
    CHECK_PREVIOUS_OP(OGL_STATE_CHANGE);

    j2d_glMatrixMode(GL_MODELVIEW);
    j2d_glLoadIdentity();
}

/**
 * Initializes the OpenGL transform state by setting the modelview transform
 * using the given matrix parameters.
 *
 * REMIND: it may be worthwhile to add serial id to AffineTransform, so we
 *         could do a quick check to see if the xform has changed since
 *         last time... a simple object compare won't suffice...
 */
void
OGLContext_SetTransform(OGLContext *oglc,
                        jdouble m00, jdouble m10,
                        jdouble m01, jdouble m11,
                        jdouble m02, jdouble m12)
{
    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_SetTransform");

    RETURN_IF_NULL(oglc);
    CHECK_PREVIOUS_OP(OGL_STATE_CHANGE);

    if (oglc->xformMatrix == NULL) {
        size_t arrsize = 16 * sizeof(GLdouble);
        oglc->xformMatrix = (GLdouble *)malloc(arrsize);
        memset(oglc->xformMatrix, 0, arrsize);
        oglc->xformMatrix[10] = 1.0;
        oglc->xformMatrix[15] = 1.0;
    }

    // copy values from AffineTransform object into native matrix array
    oglc->xformMatrix[0] = m00;
    oglc->xformMatrix[1] = m10;
    oglc->xformMatrix[4] = m01;
    oglc->xformMatrix[5] = m11;
    oglc->xformMatrix[12] = m02;
    oglc->xformMatrix[13] = m12;

    J2dTraceLn3(J2D_TRACE_VERBOSE, "  [%lf %lf %lf]",
                oglc->xformMatrix[0], oglc->xformMatrix[4],
                oglc->xformMatrix[12]);
    J2dTraceLn3(J2D_TRACE_VERBOSE, "  [%lf %lf %lf]",
                oglc->xformMatrix[1], oglc->xformMatrix[5],
                oglc->xformMatrix[13]);

    j2d_glMatrixMode(GL_MODELVIEW);
    j2d_glLoadMatrixd(oglc->xformMatrix);
}

/**
 * Creates a 2D texture of the given format and dimensions and returns the
 * texture object identifier.  This method is typically used to create a
 * temporary texture for intermediate work, such as in the
 * OGLContext_InitBlitTileTexture() method below.
 */
GLuint
OGLContext_CreateBlitTexture(GLenum internalFormat, GLenum pixelFormat,
                             GLuint width, GLuint height)
{
    GLuint texID;
    GLint sp, sr, rl, align;
    GLclampf priority = 1.0f;

    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_CreateBlitTexture");

    j2d_glGenTextures(1, &texID);
    j2d_glBindTexture(GL_TEXTURE_2D, texID);
    j2d_glPrioritizeTextures(1, &texID, &priority);
    j2d_glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    j2d_glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    OGLSD_RESET_TEXTURE_WRAP(GL_TEXTURE_2D);

    // save pixel store parameters (since this method could be invoked after
    // the caller has already set up its pixel store parameters)
    j2d_glGetIntegerv(GL_UNPACK_SKIP_PIXELS, &sp);
    j2d_glGetIntegerv(GL_UNPACK_SKIP_ROWS, &sr);
    j2d_glGetIntegerv(GL_UNPACK_ROW_LENGTH, &rl);
    j2d_glGetIntegerv(GL_UNPACK_ALIGNMENT, &align);

    // set pixel store parameters to default values
    j2d_glPixelStorei(GL_UNPACK_SKIP_PIXELS, 0);
    j2d_glPixelStorei(GL_UNPACK_SKIP_ROWS, 0);
    j2d_glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
    j2d_glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

    j2d_glTexImage2D(GL_TEXTURE_2D, 0, internalFormat,
                     width, height, 0,
                     pixelFormat, GL_UNSIGNED_BYTE, NULL);

    // restore pixel store parameters
    j2d_glPixelStorei(GL_UNPACK_SKIP_PIXELS, sp);
    j2d_glPixelStorei(GL_UNPACK_SKIP_ROWS, sr);
    j2d_glPixelStorei(GL_UNPACK_ROW_LENGTH, rl);
    j2d_glPixelStorei(GL_UNPACK_ALIGNMENT, align);

    return texID;
}

/**
 * Initializes a small texture tile for use with tiled blit operations (see
 * OGLBlitLoops.c and OGLMaskBlit.c for usage examples).  The texture ID for
 * the tile is stored in the given OGLContext.  The tile is initially filled
 * with garbage values, but the tile is updated as needed (via
 * glTexSubImage2D()) with real RGBA values used in tiled blit situations.
 * The internal format for the texture is GL_RGBA8, which should be sufficient
 * for storing system memory surfaces of any known format (see PixelFormats
 * for a list of compatible surface formats).
 */
jboolean
OGLContext_InitBlitTileTexture(OGLContext *oglc)
{
    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_InitBlitTileTexture");

    oglc->blitTextureID =
        OGLContext_CreateBlitTexture(GL_RGBA8, GL_RGBA,
                                     OGLC_BLIT_TILE_SIZE,
                                     OGLC_BLIT_TILE_SIZE);

    return JNI_TRUE;
}

/**
 * Destroys the OpenGL resources associated with the given OGLContext.
 * It is required that the native context associated with the OGLContext
 * be made current prior to calling this method.
 */
void
OGLContext_DestroyContextResources(OGLContext *oglc)
{
    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_DestroyContextResources");

    if (oglc->xformMatrix != NULL) {
        free(oglc->xformMatrix);
    }

    if (oglc->blitTextureID != 0) {
        j2d_glDeleteTextures(1, &oglc->blitTextureID);
    }
}

/**
 * Returns JNI_TRUE if the given extension name is available for the current
 * GraphicsConfig; JNI_FALSE otherwise.  An extension is considered available
 * if its identifier string is found amongst the space-delimited GL_EXTENSIONS
 * string.
 *
 * Adapted from the OpenGL Red Book, pg. 506.
 */
jboolean
OGLContext_IsExtensionAvailable(const char *extString, char *extName)
{
    jboolean ret = JNI_FALSE;
    char *p = (char *)extString;
    char *end;

    if (extString == NULL) {
        J2dTraceLn(J2D_TRACE_INFO, "OGLContext_IsExtensionAvailable");
        J2dRlsTraceLn(J2D_TRACE_ERROR,
            "OGLContext_IsExtensionAvailable: extension string is null");
        return JNI_FALSE;
    }

    end = p + strlen(p);

    while (p < end) {
        size_t n = strcspn(p, " ");

        if ((strlen(extName) == n) && (strncmp(extName, p, n) == 0)) {
            ret = JNI_TRUE;
            break;
        }

        p += (n + 1);
    }

    J2dRlsTraceLn2(J2D_TRACE_INFO,
                   "OGLContext_IsExtensionAvailable: %s=%s",
                   extName, ret ? "true" : "false");

    return ret;
}

/**
 * Returns JNI_TRUE only if all of the following conditions are met:
 *   - the GL_EXT_framebuffer_object extension is available
 *   - FBO support has been enabled via the system property
 *   - we can successfully create an FBO with depth capabilities
 */
static jboolean
OGLContext_IsFBObjectExtensionAvailable(JNIEnv *env,
                                        const char *extString)
{
    jboolean isFBObjectEnabled = JNI_FALSE;
    GLuint fbobjectID, textureID, depthID;
    jint width = 1, height = 1;

    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_IsFBObjectExtensionAvailable");

    // first see if the fbobject extension is available
    if (!OGLContext_IsExtensionAvailable(extString,
                                         "GL_EXT_framebuffer_object"))
    {
        return JNI_FALSE;
    }

    // next see if the depth texture extension is available
    if (!OGLContext_IsExtensionAvailable(extString,
                                         "GL_ARB_depth_texture"))
    {
        return JNI_FALSE;
    }

    // next see if the fbobject system property has been enabled
    isFBObjectEnabled =
        JNU_GetStaticFieldByName(env, NULL,
                                 "sun/java2d/opengl/OGLSurfaceData",
                                 "isFBObjectEnabled", "Z").z;
    if (!isFBObjectEnabled) {
        J2dRlsTraceLn(J2D_TRACE_INFO,
            "OGLContext_IsFBObjectExtensionAvailable: disabled via flag");
        return JNI_FALSE;
    }

    // finally, create a dummy fbobject with depth capabilities to see
    // if this configuration is supported by the drivers/hardware
    // (first we initialize a color texture object that will be used to
    // construct the dummy fbobject)
    j2d_glGenTextures(1, &textureID);
    j2d_glBindTexture(GL_TEXTURE_2D, textureID);
    j2d_glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB,
                     width, height, 0,
                     GL_RGB, GL_UNSIGNED_BYTE, NULL);
    j2d_glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    j2d_glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    // initialize framebuffer object using color texture created above
    if (!OGLSD_InitFBObject(&fbobjectID, &depthID,
                            textureID, GL_TEXTURE_2D,
                            width, height))
    {
        J2dRlsTraceLn(J2D_TRACE_INFO,
            "OGLContext_IsFBObjectExtensionAvailable: fbobject unsupported");
        j2d_glDeleteTextures(1, &textureID);
        return JNI_FALSE;
    }

    // delete the temporary resources
    j2d_glDeleteTextures(1, &textureID);
    j2d_glDeleteRenderbuffersEXT(1, &depthID);
    j2d_glDeleteFramebuffersEXT(1, &fbobjectID);

    J2dRlsTraceLn(J2D_TRACE_INFO,
        "OGLContext_IsFBObjectExtensionAvailable: fbobject supported");

    return JNI_TRUE;
}

/**
 * Returns JNI_TRUE only if all of the following conditions are met:
 *   - the GL_ARB_fragment_shader extension is available
 *   - the LCD text shader codepath has been enabled via the system property
 *   - the hardware supports the minimum number of texture units
 */
static jboolean
OGLContext_IsLCDShaderSupportAvailable(JNIEnv *env,
                                       jboolean fragShaderAvailable)
{
    jboolean isLCDShaderEnabled = JNI_FALSE;
    GLint maxTexUnits;

    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_IsLCDShaderSupportAvailable");

    // first see if the fragment shader extension is available
    if (!fragShaderAvailable) {
        return JNI_FALSE;
    }

    // next see if the lcdshader system property has been enabled
    isLCDShaderEnabled =
        JNU_GetStaticFieldByName(env, NULL,
                                 "sun/java2d/opengl/OGLSurfaceData",
                                 "isLCDShaderEnabled", "Z").z;
    if (!isLCDShaderEnabled) {
        J2dRlsTraceLn(J2D_TRACE_INFO,
            "OGLContext_IsLCDShaderSupportAvailable: disabled via flag");
        return JNI_FALSE;
    }

    // finally, check to see if the hardware supports the required number
    // of texture units
    j2d_glGetIntegerv(GL_MAX_TEXTURE_IMAGE_UNITS_ARB, &maxTexUnits);
    if (maxTexUnits < 4) {
        J2dRlsTraceLn1(J2D_TRACE_INFO,
          "OGLContext_IsLCDShaderSupportAvailable: not enough tex units (%d)",
          maxTexUnits);
    }

    J2dRlsTraceLn(J2D_TRACE_INFO,
        "OGLContext_IsLCDShaderSupportAvailable: LCD text shader supported");

    return JNI_TRUE;
}

/**
 * Returns JNI_TRUE only if all of the following conditions are met:
 *   - the GL_ARB_fragment_shader extension is available
 *   - the BufferedImageOp shader codepath has been enabled via the
 *     system property
 */
static jboolean
OGLContext_IsBIOpShaderSupportAvailable(JNIEnv *env,
                                        jboolean fragShaderAvailable)
{
    jboolean isBIOpShaderEnabled = JNI_FALSE;

    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_IsBIOpShaderSupportAvailable");

    // first see if the fragment shader extension is available
    if (!fragShaderAvailable) {
        return JNI_FALSE;
    }

    // next see if the biopshader system property has been enabled
    isBIOpShaderEnabled =
        JNU_GetStaticFieldByName(env, NULL,
                                 "sun/java2d/opengl/OGLSurfaceData",
                                 "isBIOpShaderEnabled", "Z").z;
    if (!isBIOpShaderEnabled) {
        J2dRlsTraceLn(J2D_TRACE_INFO,
            "OGLContext_IsBIOpShaderSupportAvailable: disabled via flag");
        return JNI_FALSE;
    }

    /*
     * Note: In theory we should probably do some other checks here, like
     * linking a sample shader to see if the hardware truly supports our
     * shader programs.  However, our current BufferedImageOp shaders were
     * designed to support first-generation shader-level hardware, so the
     * assumption is that if our shaders work on those GPUs, then they'll
     * work on newer ones as well.  Also, linking a fragment program can
     * cost valuable CPU cycles, which is another reason to avoid these
     * checks at startup.
     */

    J2dRlsTraceLn(J2D_TRACE_INFO,
        "OGLContext_IsBIOpShaderSupportAvailable: BufferedImageOp shader supported");

    return JNI_TRUE;
}

/**
 * Returns JNI_TRUE only if all of the following conditions are met:
 *   - the GL_ARB_fragment_shader extension is available
 *   - the Linear/RadialGradientPaint shader codepath has been enabled via the
 *     system property
 */
static jboolean
OGLContext_IsGradShaderSupportAvailable(JNIEnv *env,
                                        jboolean fragShaderAvailable)
{
    jboolean isGradShaderEnabled = JNI_FALSE;

    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_IsGradShaderSupportAvailable");

    // first see if the fragment shader extension is available
    if (!fragShaderAvailable) {
        return JNI_FALSE;
    }

    // next see if the gradshader system property has been enabled
    isGradShaderEnabled =
        JNU_GetStaticFieldByName(env, NULL,
                                 "sun/java2d/opengl/OGLSurfaceData",
                                 "isGradShaderEnabled", "Z").z;
    if (!isGradShaderEnabled) {
        J2dRlsTraceLn(J2D_TRACE_INFO,
            "OGLContext_IsGradShaderSupportAvailable: disabled via flag");
        return JNI_FALSE;
    }

    J2dRlsTraceLn(J2D_TRACE_INFO,
        "OGLContext_IsGradShaderSupportAvailable: Linear/RadialGradientPaint shader supported");

    return JNI_TRUE;
}

/**
 * Checks for the presence of the optional extensions used by
 * the Java 2D OpenGL pipeline.  The given caps bitfield is updated
 * to reflect the availability of these extensions.
 */
void
OGLContext_GetExtensionInfo(JNIEnv *env, jint *caps)
{
    jint vcap = OGLC_VENDOR_OTHER;
    const char *vendor = (char *)j2d_glGetString(GL_VENDOR);
    const char *e = (char *)j2d_glGetString(GL_EXTENSIONS);
    jboolean fragShaderAvail =
        OGLContext_IsExtensionAvailable(e, "GL_ARB_fragment_shader");

    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_GetExtensionInfo");

    *caps |= CAPS_TEXNONSQUARE;
    if (OGLContext_IsExtensionAvailable(e, "GL_ARB_multitexture")) {
        *caps |= CAPS_MULTITEXTURE;
    }
    if (OGLContext_IsExtensionAvailable(e, "GL_ARB_texture_non_power_of_two")){
        *caps |= CAPS_TEXNONPOW2;
    }
    // 6656574: Use of the GL_ARB_texture_rectangle extension by Java 2D
    // complicates any third-party libraries that try to interact with
    // the OGL pipeline (and we've run into driver bugs in the past related
    // to this extension), so for now we will disable its use by default (unless
    // forced). We will still make use of the GL_ARB_texture_non_power_of_two
    // extension when available, which is the better choice going forward
    // anyway.
    if (OGLContext_IsExtensionAvailable(e, "GL_ARB_texture_rectangle") &&
        getenv("J2D_OGL_TEXRECT") != NULL)
    {
        *caps |= CAPS_EXT_TEXRECT;
    }
    if (OGLContext_IsFBObjectExtensionAvailable(env, e)) {
        *caps |= CAPS_EXT_FBOBJECT;
    }
    if (OGLContext_IsLCDShaderSupportAvailable(env, fragShaderAvail)) {
        *caps |= CAPS_EXT_LCD_SHADER | CAPS_PS20;
    }
    if (OGLContext_IsBIOpShaderSupportAvailable(env, fragShaderAvail)) {
        *caps |= CAPS_EXT_BIOP_SHADER | CAPS_PS20;
    }
    if (OGLContext_IsGradShaderSupportAvailable(env, fragShaderAvail)) {
        *caps |= CAPS_EXT_GRAD_SHADER | CAPS_PS20;
    }
    if (OGLContext_IsExtensionAvailable(e, "GL_NV_fragment_program")) {
        // this is an Nvidia board, at least PS 2.0, but we can't
        // use the "max instructions" heuristic since GeForce FX
        // boards report 1024 even though they're only PS 2.0,
        // so we'll check the following, which does imply PS 3.0
        if (OGLContext_IsExtensionAvailable(e, "GL_NV_fragment_program2")) {
            *caps |= CAPS_PS30;
        }
    } else {
        // for all other boards, we look at the "max instructions"
        // count reported by the GL_ARB_fragment_program extension
        // as a heuristic for detecting PS 3.0 compatible hardware
        if (OGLContext_IsExtensionAvailable(e, "GL_ARB_fragment_program")) {
            GLint instr;
            j2d_glGetProgramivARB(GL_FRAGMENT_PROGRAM_ARB,
                                  GL_MAX_PROGRAM_INSTRUCTIONS_ARB, &instr);
            if (instr > 512) {
                *caps |= CAPS_PS30;
            }
        }
    }
    // stuff vendor descriptor in the upper bits of the caps
    if (vendor != NULL) {
        if (strncmp(vendor, "ATI", 3) == 0) {
            vcap = OGLC_VENDOR_ATI;
        } else if (strncmp(vendor, "NVIDIA", 6) == 0) {
            vcap = OGLC_VENDOR_NVIDIA;
        } else if (strncmp(vendor, "Sun", 3) == 0) {
            vcap = OGLC_VENDOR_SUN;
        }
        // REMIND: new in 7 - check if needs fixing
        *caps |= ((vcap & OGLC_VCAP_MASK) << OGLC_VCAP_OFFSET);
    }

}

/**
 * Returns JNI_TRUE if the given GL_VERSION string meets the minimum
 * requirements (>= 1.2); JNI_FALSE otherwise.
 */
jboolean
OGLContext_IsVersionSupported(const unsigned char *versionstr)
{
    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_IsVersionSupported");

    if (versionstr == NULL) {
        J2dRlsTraceLn(J2D_TRACE_ERROR,
            "OGLContext_IsVersionSupported: version string is null");
        return JNI_FALSE;
    }

    // note that this check allows for OpenGL 2.x
    return ((versionstr[0] == '1' && versionstr[2] >= '2') ||
            (versionstr[0] >= '2'));
}

/**
 * Compiles and links the given fragment shader program.  If
 * successful, this function returns a handle to the newly created shader
 * program; otherwise returns 0.
 */
GLhandleARB
OGLContext_CreateFragmentProgram(const char *fragmentShaderSource)
{
    GLhandleARB fragmentShader, fragmentProgram;
    GLint success;
    int infoLogLength = 0;

    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_CreateFragmentProgram");

    // create the shader object and compile the shader source code
    fragmentShader = j2d_glCreateShaderObjectARB(GL_FRAGMENT_SHADER_ARB);
    j2d_glShaderSourceARB(fragmentShader, 1, &fragmentShaderSource, NULL);
    j2d_glCompileShaderARB(fragmentShader);
    j2d_glGetObjectParameterivARB(fragmentShader,
                                  GL_OBJECT_COMPILE_STATUS_ARB,
                                  &success);

    // print the compiler messages, if necessary
    j2d_glGetObjectParameterivARB(fragmentShader,
                                  GL_OBJECT_INFO_LOG_LENGTH_ARB,
                                  &infoLogLength);
    if (infoLogLength > 1) {
        char infoLog[1024];
        j2d_glGetInfoLogARB(fragmentShader, 1024, NULL, infoLog);
        J2dRlsTraceLn2(J2D_TRACE_WARNING,
            "OGLContext_CreateFragmentProgram: compiler msg (%d):\n%s",
                       infoLogLength, infoLog);
    }

    if (!success) {
        J2dRlsTraceLn(J2D_TRACE_ERROR,
            "OGLContext_CreateFragmentProgram: error compiling shader");
        j2d_glDeleteObjectARB(fragmentShader);
        return 0;
    }

    // create the program object and attach it to the shader
    fragmentProgram = j2d_glCreateProgramObjectARB();
    j2d_glAttachObjectARB(fragmentProgram, fragmentShader);

    // it is now safe to delete the shader object
    j2d_glDeleteObjectARB(fragmentShader);

    // link the program
    j2d_glLinkProgramARB(fragmentProgram);
    j2d_glGetObjectParameterivARB(fragmentProgram,
                                  GL_OBJECT_LINK_STATUS_ARB,
                                  &success);

    // print the linker messages, if necessary
    j2d_glGetObjectParameterivARB(fragmentProgram,
                                  GL_OBJECT_INFO_LOG_LENGTH_ARB,
                                  &infoLogLength);
    if (infoLogLength > 1) {
        char infoLog[1024];
        j2d_glGetInfoLogARB(fragmentProgram, 1024, NULL, infoLog);
        J2dRlsTraceLn2(J2D_TRACE_WARNING,
            "OGLContext_CreateFragmentProgram: linker msg (%d):\n%s",
                       infoLogLength, infoLog);
    }

    if (!success) {
        J2dRlsTraceLn(J2D_TRACE_ERROR,
            "OGLContext_CreateFragmentProgram: error linking shader");
        j2d_glDeleteObjectARB(fragmentProgram);
        return 0;
    }

    return fragmentProgram;
}

/*
 * Class:     sun_java2d_opengl_OGLContext
 * Method:    getOGLIdString
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_sun_java2d_opengl_OGLContext_getOGLIdString
  (JNIEnv *env, jclass oglcc)
{
    char *vendor, *renderer, *version;
    char *pAdapterId;
    jobject ret = NULL;
    int len;

    J2dTraceLn(J2D_TRACE_INFO, "OGLContext_getOGLIdString");

    vendor = (char*)j2d_glGetString(GL_VENDOR);
    if (vendor == NULL) {
        vendor = "Unknown Vendor";
    }
    renderer = (char*)j2d_glGetString(GL_RENDERER);
    if (renderer == NULL) {
        renderer = "Unknown Renderer";
    }
    version = (char*)j2d_glGetString(GL_VERSION);
    if (version == NULL) {
        version = "unknown version";
    }

    // 'vendor renderer (version)0'
    len = strlen(vendor) + 1 + strlen(renderer) + 1 + 1+strlen(version)+1 + 1;
    pAdapterId = malloc(len);
    if (pAdapterId != NULL) {

        jio_snprintf(pAdapterId, len, "%s %s (%s)", vendor, renderer, version);

        J2dTraceLn1(J2D_TRACE_VERBOSE, "  id=%s", pAdapterId);

        ret = JNU_NewStringPlatform(env, pAdapterId);

        free(pAdapterId);
    }

    return ret;
}

#endif /* !HEADLESS */

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