title: no uniform with name 'u_proj' in shader
body: <p>I wrote a pair of shaders to display the textures as greyscale instead of full color. I used these shaders with libGDX's built in SpriteBatch class and it worked. Then when I tried to use it with the built in SpriteCache class it didn't work. I looked at the SpriteCache code and saw that it set some different uniforms that I tried to take into account but I seem to have gone wrong somwhere.</p>
  
  <p>The SpriteCache class in libGDX sets the following uniforms:</p>
  
  <pre><code>customShader.setUniformMatrix("u_proj", projectionMatrix);
  customShader.setUniformMatrix("u_trans", transformMatrix);
  customShader.setUniformMatrix("u_projTrans", combinedMatrix);
  customShader.setUniformi("u_texture", 0);
  </code></pre>
  
  <p>This is my vertex shader:</p>
  
  <pre><code>attribute vec4 a_position;
  attribute vec4 a_color;
  attribute vec2 a_texCoord0;
  
  uniform mat4 u_proj;
  uniform mat4 u_projTrans;
  uniform mat4 u_trans;
  
  varying vec4 v_color;
  varying vec2 v_texCoords;
  
  void main() {
      v_color = a_color;
      v_texCoords = a_texCoord0;
      gl_Position = a_position* u_proj * u_trans;
  }
  </code></pre>
  
  <p>and this is the fragment shader:</p>
  
  <pre><code>varying vec4 v_color;
  varying vec2 v_texCoords;
  uniform sampler2D u_texture;
  uniform u_projTrans;
  void main() {
          vec4 color = texture2D(u_texture, v_texCoords).rgba;
          float gray = (color.r + color.g + color.b) / 3.0;
          vec3 grayscale = vec3(gray + 0* u_projTrans[0][0]);
          gl_FragColor = vec4(grayscale, color.a);
  }
  </code></pre>
  
  <p>The error I get is:</p>
  
  <pre><code>Exception in thread "LWJGL Application" java.lang.IllegalArgumentException: no uniform with name 'u_proj' in shader
  ...
  com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:206)
      at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:114)ackends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:206)
      at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:114)
  </code></pre>
  
  <p>I guess do any of you guys know why this isn't working? There is a uniform with the name u_proj.
  Thank you all!</p>