libgdx使用过渡精灵

Question

i found some transition sprite and want to use them in my programm. It's just a black and white picture.

How can I get every pixel under a brightness value from this sprite and draw these pixel black, to get an animation?

I tried something like this:

sr.begin(ShapeType.Filled);
    sr.setColor(0, 0, 0, 1f);
    for(int y = 0; y < 320; y ++) {
        for(int x = 0; x < 531; x ++) {
            transSprite.getTexture().getTextureData().prepare();
            int brightness = transSprite.getTexture().getTextureData().consumePixmap().getPixel(x, y);

            if(brightness <= alpha * 255) {
                sr.rect(x, y, 1, 1);
            }
        }
    }
    sr.end();

But this is too slow.

I have a resolution of 531 x 320 Pixel and an alpha value between 0 and 1 for the animation.

Do you have any ideas?

Answer 1

This can be done with your shader. Make a custom shader with a threshold value to use with SpriteBatch. I copied the default sprite batch shader, but changed the fragment shader part.

String vertexShader = "attribute vec4 " + ShaderProgram.POSITION_ATTRIBUTE + ";\n" //
            + "attribute vec4 " + ShaderProgram.COLOR_ATTRIBUTE + ";\n" //
            + "attribute vec2 " + ShaderProgram.TEXCOORD_ATTRIBUTE + "0;\n" //
            + "uniform mat4 u_projTrans;\n" //
            + "varying vec4 v_color;\n" //
            + "varying vec2 v_texCoords;\n" //
            + "\n" //
            + "void main()\n" //
            + "{\n" //
            + "   v_color = " + ShaderProgram.COLOR_ATTRIBUTE + ";\n" //
            + "   v_texCoords = " + ShaderProgram.TEXCOORD_ATTRIBUTE + "0;\n" //
            + "   gl_Position =  u_projTrans * " + ShaderProgram.POSITION_ATTRIBUTE + ";\n" //
            + "}\n";
        String fragmentShader = "#ifdef GL_ES\n" //
            + "#define LOWP lowp\n" //
            + "precision mediump float;\n" //
            + "#else\n" //
            + "#define LOWP \n" //
            + "#endif\n" //
            + "varying LOWP vec4 v_color;\n" //
            + "varying vec2 v_texCoords;\n" //
            + "uniform sampler2D u_texture;\n" //
            + "uniform float u_threshold;\n" //
            + "void main()\n"//
            + "{\n" //
            + "  vec4 texture = texture2D(u_texture, v_texCoords);\n" //
            + "  gl_FragColor = v_color * step(u_threshold, texture.r);\n" //
            + "}";

        customShader = new ShaderProgram(vertexShader, fragmentShader);

Then you can animate it by changing the u_threshold value.

spriteBatch.setShader(customShader);
spriteBatch.begin();
customShader.setUniformf("u_threshold", brightness); //where brightness is from 0 to 1
spriteBatch.draw(sprite);
spriteBatch.end();