剪刀测试

剪刀测试可限制屏幕的某一部分更新，其他部分不更新。实例代码如下：

public class MyRenderer implements Renderer {

	
	public MyRenderer(Context ctx) {

	}
	
	@Override
	public void onDrawFrame(GL10 gl) {
		
        // Clear blue window
        gl.glClearColor(0.0f, 0.0f, 1.0f, 0.0f);
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
        
        // Now set scissor to smaller red sub region
        gl.glClearColor(1.0f, 0.0f, 0.0f, 0.0f);
        gl.glScissor(100, 100, 600, 400);
        gl.glEnable(GL10.GL_SCISSOR_TEST);
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
        
        // Finally, an even smaller green rectangle
        gl.glClearColor(0.0f, 1.0f, 0.0f, 0.0f);
        gl.glScissor(200, 200, 400, 200);
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
        
        // Turn scissor back off for next render
        gl.glDisable(GL10.GL_SCISSOR_TEST);

	}

	@Override
	public void onSurfaceChanged(GL10 gl, int w, int h) {
	    float aspectRatio;
	    float windowWidth;
	    float windowHeight;

	    // Prevent a divide by zero
	    if(h == 0)
	        h = 1;
			
	    // Set Viewport to window dimensions
	    gl.glViewport(0, 0, w, h);

	    // Reset coordinate system
	    gl.glMatrixMode(GL10.GL_PROJECTION);
	    gl.glLoadIdentity();

	    // Establish clipping volume (left, right, bottom, top, near, far)
	    aspectRatio = (float)w / (float)h;
	    if (w <= h) 
	        {
	        windowWidth = 100;
	        windowHeight = 100 / aspectRatio;
	        gl.glOrthof(-100.0f, 100.0f, -windowHeight, windowHeight, 1.0f, -1.0f);
	        }
	    else 
	        {
	        windowWidth = 100 * aspectRatio;
	        windowHeight = 100;
	        gl.glOrthof(-windowWidth, windowWidth, -100.0f, 100.0f, 1.0f, -1.0f);
	        }

	    gl.glMatrixMode(GL10.GL_MODELVIEW);
	    gl.glLoadIdentity();
	}

	@Override
	public void onSurfaceCreated(GL10 gl, EGLConfig config) {
		// TODO Auto-generated method stub
		gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);  
		// Enable Smooth Shading, default not really needed.
		gl.glShadeModel(GL10.GL_SMOOTH);		

	}

}