[英]libgdx - blendFunc for brush line drawing? (additive/non-additive mixture)
對於兩點之間的一行中的每一步,我在每個像素處將幀精靈繪制到幀緩沖區,但是我有一個混合問題:
我目前正在使用:
(GL_ONE,GL_ONE_MINUS_SRC_ALPHA);
然后,在我的着色器中,我做:
if( color.a == 0 )
color.rgb = 0;
但是,如果你看一下紅色和綠色的星,你可以看到“加性混合”,它發生在α在(0,1)的區間之間。
沒有添加劑混合,這種3D效果發生:
有沒有辦法添加相似顏色的添加劑,但避免顏色不匹配?
它應該如下所示:
你可以使用預乘alpha來做到這一點。
首先,您需要正確設置紋理。 像這樣在黑色上畫白:
然后將紋理的亮度復制到其Alpha通道中。 在GIMP中,您可以通過右鍵單擊圖層,選擇“添加圖層蒙版”,然后選擇“圖層的灰度副本”來完成此操作。 它看起來有點像這樣(如Gimp所示):
然后,如果你願意,你可以重新着色它的RGB通道,雖然它更通用,讓它在你的代碼中保持白色並着色。
在你的代碼中,當你繪制形狀時,使用混合函數預乘alpha:
batch.setBlendFunction(GL20.GL_ONE, GL20.GL_ONE_MINUS_SRC_ALPHA);
並使用默認的SpriteBatch着色器繪制它。 繪制完形狀后,切換回常規Alpha混合:
batch.setBlendFunction(GL20.GL_SRC_ALPHA, GL20.GL_ONE_MINUS_SRC_ALPHA);
游戲示例:
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;
}
}
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