Android example source code file (LinearGradient.java)

This example Android source code file (LinearGradient.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Android by Example" ^TM.

Java - Android tags/keywords

gradientshader, lineargradient, lineargradientpaint, lineargradientpaintcontext, override, tilemode

The LinearGradient.java Android example source code

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.graphics;

public class LinearGradient extends GradientShader {

    private java.awt.Paint mJavaPaint;

    /**
     * Create a shader that draws a linear gradient along a line.
     *
     * @param x0 The x-coordinate for the start of the gradient line
     * @param y0 The y-coordinate for the start of the gradient line
     * @param x1 The x-coordinate for the end of the gradient line
     * @param y1 The y-coordinate for the end of the gradient line
     * @param colors The colors to be distributed along the gradient line
     * @param positions May be null. The relative positions [0..1] of each
     *            corresponding color in the colors array. If this is null, the
     *            the colors are distributed evenly along the gradient line.
     * @param tile The Shader tiling mode
     */
    public LinearGradient(float x0, float y0, float x1, float y1, int colors[], float positions[],
            TileMode tile) {
        super(colors, positions);
        mJavaPaint = new LinearGradientPaint(x0, y0, x1, y1, mColors, mPositions, tile);
    }

    /**
     * Create a shader that draws a linear gradient along a line.
     *
     * @param x0 The x-coordinate for the start of the gradient line
     * @param y0 The y-coordinate for the start of the gradient line
     * @param x1 The x-coordinate for the end of the gradient line
     * @param y1 The y-coordinate for the end of the gradient line
     * @param color0 The color at the start of the gradient line.
     * @param color1 The color at the end of the gradient line.
     * @param tile The Shader tiling mode
     */
    public LinearGradient(float x0, float y0, float x1, float y1, int color0, int color1,
            TileMode tile) {
        this(x0, y0, x1, y1, new int[] { color0, color1}, null /*positions*/, tile);
    }

    // ---------- Custom Methods

    @Override
    java.awt.Paint getJavaPaint() {
        return mJavaPaint;
    }

    /**
     * Linear Gradient (Java) Paint able to handle more than 2 points, as
     * {@link java.awt.GradientPaint} only supports 2 points and does not support Android's tile
     * modes.
     */
    private static class LinearGradientPaint extends GradientPaint {

        private final float mX0;
        private final float mY0;
        private final float mDx;
        private final float mDy;
        private final float mDSize2;

        public LinearGradientPaint(float x0, float y0, float x1, float y1, int colors[],
                float positions[], TileMode tile) {
            super(colors, positions, tile);
                mX0 = x0;
                mY0 = y0;
                mDx = x1 - x0;
                mDy = y1 - y0;
                mDSize2 = mDx * mDx + mDy * mDy;
        }

        public java.awt.PaintContext createContext(
                java.awt.image.ColorModel      colorModel,
                java.awt.Rectangle             deviceBounds,
                java.awt.geom.Rectangle2D      userBounds,
                java.awt.geom.AffineTransform  xform,
                java.awt.RenderingHints        hints) {
            precomputeGradientColors();
            return new LinearGradientPaintContext(colorModel);
        }

        private class LinearGradientPaintContext implements java.awt.PaintContext {

            private final java.awt.image.ColorModel mColorModel;

            public LinearGradientPaintContext(java.awt.image.ColorModel colorModel) {
                mColorModel = colorModel;
                // FIXME: so far all this is always the same rect gotten in getRaster with an indentity matrix?
            }

            public void dispose() {
            }

            public java.awt.image.ColorModel getColorModel() {
                return mColorModel;
            }

            public java.awt.image.Raster getRaster(int x, int y, int w, int h) {
                java.awt.image.BufferedImage image = new java.awt.image.BufferedImage(w, h,
                        java.awt.image.BufferedImage.TYPE_INT_ARGB);

                int[] data = new int[w*h];

                if (mDx == 0) { // vertical gradient
                    // compute first column and copy to all other columns
                    int index = 0;
                    for (int iy = 0 ; iy < h ; iy++) {
                        int color = getColor(iy + y, mY0, mDy);
                        for (int ix = 0 ; ix < w ; ix++) {
                            data[index++] = color;
                        }
                    }
                } else if (mDy == 0) { // horizontal
                    // compute first line in a tmp array and copy to all lines
                    int[] line = new int[w];
                    for (int ix = 0 ; ix < w ; ix++) {
                        line[ix] = getColor(ix + x, mX0, mDx);
                    }

                    for (int iy = 0 ; iy < h ; iy++) {
                        System.arraycopy(line, 0, data, iy*w, line.length);
                    }
                } else {
                    int index = 0;
                    for (int iy = 0 ; iy < h ; iy++) {
                        for (int ix = 0 ; ix < w ; ix++) {
                            data[index++] = getColor(ix + x, iy + y);
                        }
                    }
                }

                image.setRGB(0 /*startX*/, 0 /*startY*/, w, h, data, 0 /*offset*/, w /*scansize*/);

                return image.getRaster();
            }
        }

        /** Returns a color for the easy vertical/horizontal mode */
        private int getColor(float absPos, float refPos, float refSize) {
            float pos = (absPos - refPos) / refSize;

            return getGradientColor(pos);
        }

        /**
         * Returns a color for an arbitrary point.
         */
        private int getColor(float x, float y) {
            // find the x position on the gradient vector.
            float _x = (mDx*mDy*(y-mY0) + mDy*mDy*mX0 + mDx*mDx*x) / mDSize2;
            // from it get the position relative to the vector
            float pos = (float) ((_x - mX0) / mDx);

            return getGradientColor(pos);
        }
    }
}