LibGDX - B/W图像将黑色渲染为透明，将白色渲染为黑色

String vertexShader =
        "attribute vec4 a_position; \n" +
        "attribute vec4 a_color;\n" +
        "attribute vec2 a_texCoord0;\n" +
        "varying vec4 v_color;" +
        "varying vec2 v_texCoords;" +
        "void main()                  \n" +
        "{                            \n" +
        "   v_color = vec4(1, 1, 1, 1); \n" +
        "   v_texCoords = a_texCoord0; \n" +
        "   gl_Position =  u_projTrans * a_position;  \n"      +
        "}                            \n";

String fragmentShader =
        "#ifdef GL_ES\n" +
        "precision mediump float;\n" +
        "#endif\n" +
        "uniform sampler2D u_texture;\n" +
        "varying vec4 v_color;\n" +
        "varying vec2 v_texCoords;\n" +
        "void main()                                  \n" +
        "{                                            \n" +
        "  vec4 color = texture2D(u_texture, v_texCoords);\n" +
        "  if(color == vec4(0, 0, 0, 1)) \n" +
        "    gl_FragColor = vec4(0, 0, 0, 0);\n" +
        "  else if(color == vec4(1, 1, 1, 1)) \n" +
        "    gl_FragColor = vec4(0, 0, 0, 1);\n" +
        "  else \n" +
        "    gl_FragColor = color;\n" +
        "}                                            \n";

ShaderProgram shader = new ShaderProgram(vertexShader, fragmentShader);

SpriteBatch batch = new SpriteBatch();
Texture texture = new Texture("image.png");
TextureRegion region = new TextureRegion(texture);

batch.setShader(shader);
batch.begin();
batch.draw(region, 0, 0);
batch.end();

batch.setShader(null); // 恢复默认Shader