在着色器中旋转，移动和缩放蒙版

Question

我想在着色器中移动（或其他动作）一个遮罩。但我不知道如何在着色器中执行这些操作。

我的代码：

@Override
public void create() {        
    batch = new SpriteBatch();

    background = new Texture(Gdx.files.internal("images/background.png"));
    spritebackgournd = new Sprite(background,Gdx.graphics.getWidth(),Gdx.graphics.getHeight());

    foreground = new Texture(Gdx.files.internal("images/foreground.png"));
    mask = new Texture(Gdx.files.internal("images/mask.png"));

     spriteforegournd = new Sprite(foreground,Gdx.graphics.getWidth(),Gdx.graphics.getHeight());        

    shader = new ShaderProgram(Gdx.files.internal("shaders/shader1.vert"), Gdx.files.internal("shaders/shader1.frag"));
}

@Override
public void render() {        


    batch.begin();
    spritebackgournd.draw(batch);
     batch.setShader(shader);
        Gdx.graphics.getGL20().glActiveTexture(GL20.GL_TEXTURE0);
        spriteforegournd.getTexture().bind(0);
        //texture.bind(0);
        shader.setUniformi("u_texture", 0);
        Gdx.graphics.getGL20().glActiveTexture(GL20.GL_TEXTURE1);
        //spritemask.getTexture().bind(1);
        mask.bind(1);
        shader.setUniformi("u_mask", 1);
        Gdx.graphics.getGL20().glActiveTexture(GL20.GL_TEXTURE0);
        spriteforegournd.draw(batch);
        batch.end();
        batch.setShader(null);


}

顶点着色器：

attribute vec4 a_position;
attribute vec4 a_color;
attribute vec2 a_texCoord0;

uniform mat4 u_projTrans;

varying vec2 v_texCoords;

void main() {
v_texCoords = a_texCoord0;
gl_Position = u_projTrans * a_position;
}

片段着色器：

varying vec2 v_texCoords;
uniform sampler2D u_texture;
uniform sampler2D u_mask;
uniform mat4 u_projTrans;

void main() {
vec4 texColor = texture2D(u_texture, v_texCoords);
vec4 maskColor = texture2D(u_mask, v_texCoords);

gl_FragColor = texColor * maskColor.a;
}

我希望能够在着色器中缩放，旋转和移动蒙版。我该怎么做？