Android4.2.2 Gallery2源码分析(4)——GLCanvas.java

首先申明，找到这个类是在GLRootView.java中发现的线索。这是一个接口，源码中对该接口作了详细的说明：

//
// GLCanvas gives a convenient interface to draw using OpenGL.
//
// When a rectangle is specified in this interface, it means the region
// [x, x+width) * [y, y+height)
//
public interface GLCanvas {
    // Tells GLCanvas the size of the underlying GL surface. This should be
    // called before first drawing and when the size of GL surface is changed.
    // This is called by GLRoot and should not be called by the clients
    // who only want to draw on the GLCanvas. Both width and height must be
    // nonnegative.
    public void setSize(int width, int height);

    public void setSize(int x, int y, int width, int height);

    public void clearBuffer();
    public void clearBuffer(float[] argb);

    public void setAlpha(float alpha);
    public float getAlpha();

    public void multiplyAlpha(float alpha);

    public void translate(float x, float y, float z);
    public void translate(float x, float y);
    public void scale(float sx, float sy, float sz);
    public void rotate(float angle, float x, float y, float z);
    public void multiplyMatrix(float[] mMatrix, int offset);

    public void save();

    public void save(int saveFlags);

    public static final int SAVE_FLAG_ALL = 0xFFFFFFFF;
    public static final int SAVE_FLAG_ALPHA = 0x01;
    public static final int SAVE_FLAG_MATRIX = 0x02;

    public void restore();

    // Draws a line using the specified paint from (x1, y1) to (x2, y2).
    // (Both end points are included).
    public void drawLine(float x1, float y1, float x2, float y2, GLPaint paint);

    // Draws a rectangle using the specified paint from (x1, y1) to (x2, y2).
    // (Both end points are included).
    public void drawRect(float x1, float y1, float x2, float y2, GLPaint paint);

    // Fills the specified rectangle with the specified color.
    public void fillRect(float x, float y, float width, float height, int color);

    // Draws a texture to the specified rectangle.
    public void drawTexture(
            BasicTexture texture, int x, int y, int width, int height);
    public void drawMesh(BasicTexture tex, int x, int y, int xyBuffer,
            int uvBuffer, int indexBuffer, int indexCount);

    // Draws the source rectangle part of the texture to the target rectangle.
    public void drawTexture(BasicTexture texture, RectF source, RectF target);

    // Draw a texture with a specified texture transform.
    public void drawTexture(BasicTexture texture, float[] mTextureTransform,
                int x, int y, int w, int h);

    // Draw two textures to the specified rectangle. The actual texture used is
    // from * (1 - ratio) + to * ratio
    // The two textures must have the same size.
    public void drawMixed(BasicTexture from, int toColor,
            float ratio, int x, int y, int w, int h);

    // Draw a region of a texture and a specified color to the specified
    // rectangle. The actual color used is from * (1 - ratio) + to * ratio.
    // The region of the texture is defined by parameter "src". The target
    // rectangle is specified by parameter "target".
    public void drawMixed(BasicTexture from, int toColor,
            float ratio, RectF src, RectF target);

    public GL11 getGLInstance();

    public boolean unloadTexture(BasicTexture texture);

    public void deleteBuffer(int bufferId);

    public void deleteRecycledResources();

    public void dumpStatisticsAndClear();

    public void beginRenderTarget(RawTexture texture);

    public void endRenderTarget();
}

这里留下了我觉得与最终布局形成有比较直接关系的地方的注释(完整内容可查看源码)，从这些注释中，我意识到Gallery的布局之所以不同我之前所见的那些布局视图，是因为这里使用了OpenGL，并且使用了OpenGL材质渲染，那么不能根据以往的经验直接找到视图也就不足为奇了，因为OpenGL是在代码中一点一点画出来的，因此所有的布局视图都要到代码中去发现和寻找。