Libgdx中裁剪

 OpenGL提供了 void glScissor(GLint x,  GLint y,  GLsizei width,  GLsizei height  );  

  函数来实现裁剪功能。

  在Libgdx中，同样提供了对应的接口：ScissorStack提供的函数: pushScissor函数

/** Pushes a new scissor {@link Rectangle} onto the stack, merging it with the current top of the stack. The minimal area of
	 * overlap between the top of stack rectangle and the provided rectangle is pushed onto the stack. This will invoke
	 * {@link GLCommon#glScissor(int, int, int, int)} with the final top of stack rectangle. In case no scissor is yet on the stack
	 * this will also enable {@link GL10#GL_SCISSOR_TEST} automatically.
	 * @return true if the scissors were pushed. false if the scissor area was zero, in this case the scissors were not pushed and
	 *         no drawing should occur. */
	public static boolean pushScissors (Rectangle scissor) {
		fix(scissor);

		if (scissors.size == 0) {
			if (scissor.width < 1 || scissor.height < 1) return false;
			Gdx.gl.glEnable(GL10.GL_SCISSOR_TEST);
		} else {
			// merge scissors
			Rectangle parent = scissors.get(scissors.size - 1);
			float minX = Math.max(parent.x, scissor.x);
			float maxX = Math.min(parent.x + parent.width, scissor.x + scissor.width);
			if (maxX - minX < 1) return false;

			float minY = Math.max(parent.y, scissor.y);
			float maxY = Math.min(parent.y + parent.height, scissor.y + scissor.height);
			if (maxY - minY < 1) return false;

			scissor.x = minX;
			scissor.y = minY;
			scissor.width = maxX - minX;
			scissor.height = Math.max(1, maxY - minY);
		}
		scissors.add(scissor);
		Gdx.gl.glScissor((int)scissor.x, (int)scissor.y, (int)scissor.width, (int)scissor.height);
		return true;
	}

popScissors函数：

/** Pops the current scissor rectangle from the stack and sets the new scissor area to the new top of stack rectangle. In case
	 * no more rectangles are on the stack, {@link GL10#GL_SCISSOR_TEST} is disabled. */
	public static Rectangle popScissors () {
		Rectangle old = scissors.pop();
		if (scissors.size == 0)
			Gdx.gl.glDisable(GL10.GL_SCISSOR_TEST);
		else {
			Rectangle scissor = scissors.peek();
			Gdx.gl.glScissor((int)scissor.x, (int)scissor.y, (int)scissor.width, (int)scissor.height);
		}
		return old;
	}

通过重写Actor的draw方法就可以实现裁剪功能，例如：

@Override
	public void draw(SpriteBatch batch, float parentAlpha) {
		if(ScissorStack.pushScissors(mScissor)) {
			super.draw(batch, parentAlpha);
			ScissorStack.popScissors();
		}
	}

此功能可用来只画我们需要的区域来提高性能或是遮罩功能。