您可以使用预乘alpha来完成此操作。
首先,您需要正确设置纹理。将其绘制成黑白相间的形式,如下所示:
然后,将纹理的亮度复制到它的alpha通道中。在GIMP中,您可以右键单击图层,选择添加图层蒙版,然后选择“灰度复制层”。它看起来有点像这样(如Gimp所示):
然后,如果需要,您可以重新着色RGB通道,尽管在代码中将其保留为白色并对其进行着色更加灵活。
在代码中,当您绘制形状时,请使用预乘alpha的混合函数:
batch.setBlendFunction(GL20.GL_ONE, GL20.GL_ONE_MINUS_SRC_ALPHA)
使用默认的SpriteBatch着色器绘制它。在绘制完形状后,切换回常规的alpha混合:
batch.setBlendFunction(GL20.GL_SRC_ALPHA, GL20.GL_ONE_MINUS_SRC_ALPHA)
示例游戏:
![这里输入图片描述](https://istack.dev59.com/XvZrn.webp)
public class GameMain extends ApplicationAdapter implements InputProcessor{
SpriteBatch batch;
Texture star;
Color color = new Color();
Viewport viewport;
int screenWidth, screenHeight;
FrameBuffer fbo;
boolean shouldClearFBO = false;
boolean fboUpdated = false;
OrthographicCamera fullScreenCamera;
boolean touchDown = false;
Vector2 touchLocation = new Vector2();
int colorIndex = 0;
static final int[] COLORS = {0xff0000ff, 0x00ff00ff, 0x0000ffff, 0xffff00ff, 0xff00ffff, 0x00ffffff, 0xffffffff};
static final float SIZE = 150;
@Override
public void create () {
batch = new SpriteBatch();
star = new Texture("star.png");
viewport = new ExtendViewport(800, 480);
fullScreenCamera = new OrthographicCamera();
Gdx.input.setInputProcessor(this);
}
@Override
public void resize (int width, int height){
viewport.update(width, height, true);
fullScreenCamera.setToOrtho(false, width, height);
fullScreenCamera.position.set(width/2, height/2, 0);
fullScreenCamera.update();
fboUpdated = false;
screenWidth = width;
screenHeight = height;
}
@Override
public void render () {
if (!fboUpdated){
fboUpdated = true;
if (fbo!=null)
fbo.dispose();
fbo = new FrameBuffer(Pixmap.Format.RGBA8888, screenWidth, screenHeight, false);
fbo.begin();
Gdx.gl.glClearColor(0, 0, 0, 1);
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
fbo.end();
}
color.set(COLORS[colorIndex]);
fbo.begin();
if (shouldClearFBO){
shouldClearFBO = false;
Gdx.gl.glClearColor(0, 0, 0, 1);
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
}
if (touchDown){
batch.setProjectionMatrix(viewport.getCamera().combined);
batch.setBlendFunction(GL20.GL_ONE, GL20.GL_ONE_MINUS_SRC_ALPHA);
batch.begin();
batch.setColor(color);
batch.draw(star, touchLocation.x - SIZE/2, touchLocation.y - SIZE/2, SIZE, SIZE);
batch.end();
}
fbo.end();
Gdx.gl.glClearColor(0, 0, 0, 1);
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
batch.setColor(Color.WHITE);
batch.setProjectionMatrix(fullScreenCamera.combined);
batch.setBlendFunction(GL20.GL_ALPHA, GL20.GL_ONE_MINUS_SRC_ALPHA);
batch.begin();
batch.draw(fbo.getColorBufferTexture(), 0, screenHeight, screenWidth, -screenHeight);
batch.end();
}
@Override
public boolean keyDown(int keycode) {
switch (keycode){
case Input.Keys.SPACE:
colorIndex = (++colorIndex) % COLORS.length;
return true;
case Input.Keys.X:
shouldClearFBO = true;
return true;
}
return false;
}
@Override
public boolean keyUp(int keycode) {
return false;
}
@Override
public boolean keyTyped(char character) {
return false;
}
@Override
public boolean touchDown(int screenX, int screenY, int pointer, int button) {
viewport.unproject(touchLocation.set(screenX, screenY));
if (pointer==1){
colorIndex = (++colorIndex) % COLORS.length;
return true;
}
if (pointer == 2){
shouldClearFBO = true;
return true;
}
touchDown = true;
return true;
}
@Override
public boolean touchUp(int screenX, int screenY, int pointer, int button) {
touchDown = false;
return true;
}
@Override
public boolean touchDragged(int screenX, int screenY, int pointer) {
viewport.unproject(touchLocation.set(screenX, screenY));
return true;
}
@Override
public boolean mouseMoved(int screenX, int screenY) {
return false;
}
@Override
public boolean scrolled(int amount) {
return false;
}
}