使用OpenGl ES 2.0进行模板处理

Question

我试图找出一种方法来切出背景纹理的某个区域,以便在屏幕上不为该背景渲染某个自定义图案.例如:

这个方块可以是任何图案.我正在使用Frame Buffer Object和Stencil Buffer来实现这种效果.这是代码:

fbo.begin();
//Disables ColorMask and DepthMask so that all the rendering is done on the Stencil Buffer
Gdx.gl20.glColorMask(false, false, false, false);
Gdx.gl20.glDepthMask(false);
Gdx.gl20.glEnable(GL20.GL_STENCIL_TEST);
Gdx.gl20.glStencilFunc(GL20.GL_ALWAYS, 1, 0xFFFFFFFF);
Gdx.gl20.glStencilOp(GL20.GL_REPLACE, GL20.GL_REPLACE, GL20.GL_REPLACE);

stage.getSpriteBatch().begin();
rHeart.draw(stage.getSpriteBatch(), 1); //Draws the required pattern on the stencil buffer

//Enables the ColorMask and DepthMask to resume normal rendering
Gdx.gl20.glColorMask(true, true, true, true);
Gdx.gl20.glDepthMask(true);

Gdx.gl20.glStencilFunc(GL20.GL_EQUAL, 1, 0xFFFFFFFF);
Gdx.gl20.glStencilOp(GL20.GL_KEEP, GL20.GL_KEEP, GL20.GL_KEEP);

background.draw(stage.getSpriteBatch(), 1); //Draws the background such that the background is not rendered on the required pattern, leaving that area black.

stage.getSpriteBatch().end();
Gdx.gl20.glDisable(GL20.GL_STENCIL_TEST);
fbo.end();

然而,这根本不起作用.我怎么能用Stencil Buffers做到这一点？我也很难理解glStencilFunc和glStencilOp.如果有人能够对这两者有所了解,那将是非常有帮助的.

更新:我也尝试使用glColorMask生成相同类型的东西.这是代码:

Gdx.gl20.glClearColor(0, 0, 0, 0);
stage.draw();
FrameBuffer.clearAllFrameBuffers(Gdx.app);
fbo1.begin();
Gdx.gl20.glClearColor(0, 0, 0, 0);
batch.begin();
rubber.draw(batch, 1);
Gdx.gl20.glColorMask(false, false, false, true);
coverHeart.draw(batch, 1);
Gdx.gl20.glColorMask(true, true, true, false);
batch.end();        
fbo1.end();

toDrawHeart = new Image(new TextureRegion(fbo1.getColorBufferTexture()));
batch.begin();
toDrawHeart.draw(batch, 1);
batch.end();

这段代码产生了这个: 而不是这样的事情:(忽略窗户大小和色调)

注意:我正在使用libgdx库.

Answer 1

在绘制到a时SpriteBatch,状态更改将被忽略,直到end()被调用.如果要使用模板SpriteBatch,则需要拆分批量绘图.有一点,我遗漏了FBO,但这不应该有所作为.

@Override
public void create() {      
    camera = new OrthographicCamera(1, 1);
    batch = new SpriteBatch();

    texture = new Texture(Gdx.files.internal("data/badlogic.jpg"));
    texture.setFilter(TextureFilter.Linear, TextureFilter.Linear);

    TextureRegion region = new TextureRegion(texture, 0, 0, 256, 256);

    sprite = new Sprite(region);
    sprite.setSize(1f, 1f);
    sprite.setPosition(-0.5f, -0.5f);

    spriteUpsideDown = new Sprite(new TextureRegion(texture, 1f, 1f, 0f, 0f));
    spriteUpsideDown.setSize(1f, 1f);
    spriteUpsideDown.setPosition(-0.5f, -0.5f);

    pattern = new Sprite(region);
    pattern.setSize(0.5f, 0.5f);
    pattern.setPosition(-0.25f, -0.25f);

    << Set Input Processor >>
}

输入处理器允许设置两个布尔标志breakBatch1和breakBatch2键盘(桌面上的libgdx),用于打破SpriteBatch绘图.

@Override
public void render() {      
    Gdx.gl.glClearColor(1, 1, 1, 1);
    Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_STENCIL_BUFFER_BIT);
    batch.setProjectionMatrix(camera.combined);

    // setup drawing to stencil buffer
    Gdx.gl20.glEnable(GL20.GL_STENCIL_TEST);
    Gdx.gl20.glStencilFunc(GL20.GL_ALWAYS, 0x1, 0xffffffff);
    Gdx.gl20.glStencilOp(GL20.GL_REPLACE, GL20.GL_REPLACE, GL20.GL_REPLACE);
    Gdx.gl20.glColorMask(false, false, false, false);

    // draw base pattern
    batch.begin();
    pattern.draw(batch);

    if(breakBatch1) { batch.end(); batch.begin(); }

    // fix stencil buffer, enable color buffer
    Gdx.gl20.glColorMask(true, true, true, true);
    Gdx.gl20.glStencilOp(GL20.GL_KEEP, GL20.GL_KEEP, GL20.GL_KEEP);

    // draw where pattern has NOT been drawn
    Gdx.gl20.glStencilFunc(GL20.GL_NOTEQUAL, 0x1, 0xff);
    sprite.draw(batch);

    if(breakBatch2) { batch.end(); batch.begin(); }

    // draw where pattern HAS been drawn.
    Gdx.gl20.glStencilFunc(GL20.GL_EQUAL, 0x1, 0xff);
    spriteUpsideDown.draw(batch);
    batch.end();
}