Android example source code file (SweepGradient.java)

This example Android source code file (SweepGradient.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, override, sweepgradient, sweepgradientpaint, sweepgradientpaintcontext

The SweepGradient.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 SweepGradient extends GradientShader {

    private SweepGradientPaint mPaint;

    /**
     * A subclass of Shader that draws a sweep gradient around a center point.
     *
     * @param cx       The x-coordinate of the center
     * @param cy       The y-coordinate of the center
     * @param colors   The colors to be distributed between around the center.
     *                 There must be at least 2 colors in the array.
     * @param positions May be NULL. The relative position of
     *                 each corresponding color in the colors array, beginning
     *                 with 0 and ending with 1.0. If the values are not
     *                 monotonic, the drawing may produce unexpected results.
     *                 If positions is NULL, then the colors are automatically
     *                 spaced evenly.
     */
    public SweepGradient(float cx, float cy,
                         int colors[], float positions[]) {
        super(colors, positions);

        mPaint = new SweepGradientPaint(cx, cy, mColors, mPositions);
    }

    /**
     * A subclass of Shader that draws a sweep gradient around a center point.
     *
     * @param cx       The x-coordinate of the center
     * @param cy       The y-coordinate of the center
     * @param color0   The color to use at the start of the sweep
     * @param color1   The color to use at the end of the sweep
     */
    public SweepGradient(float cx, float cy, int color0, int color1) {
        this(cx, cy, new int[] { color0, color1}, null /*positions*/);
    }

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

    private static class SweepGradientPaint extends GradientPaint {

        private final float mCx;
        private final float mCy;

        public SweepGradientPaint(float cx, float cy, int[] colors, float[] positions) {
            super(colors, positions, null /*tileMode*/);
            mCx = cx;
            mCy = cy;
        }

        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 SweepGradientPaintContext(colorModel);
        }

        private class SweepGradientPaintContext implements java.awt.PaintContext {

            private final java.awt.image.ColorModel mColorModel;

            public SweepGradientPaintContext(java.awt.image.ColorModel colorModel) {
                mColorModel = colorModel;
            }

            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];

                // compute angle from each point to the center, and figure out the distance from
                // it.
                int index = 0;
                for (int iy = 0 ; iy < h ; iy++) {
                    for (int ix = 0 ; ix < w ; ix++) {
                        float dx = x + ix - mCx;
                        float dy = y + iy - mCy;
                        float angle;
                        if (dx == 0) {
                            angle = (float) (dy < 0 ? 3 * Math.PI / 2 : Math.PI / 2);
                        } else if (dy == 0) {
                            angle = (float) (dx < 0 ? Math.PI : 0);
                        } else {
                            angle = (float) Math.atan(dy / dx);
                            if (dx > 0) {
                                if (dy < 0) {
                                    angle += Math.PI * 2;
                                }
                            } else {
                                angle += Math.PI;
                            }
                        }

                        // convert to 0-1. value and get color
                        data[index++] = getGradientColor((float) (angle / (2 * Math.PI)));
                    }
                }

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

                return image.getRaster();
            }

        }
    }

}