iOS5上的GLKit：设置纹理可防止其他绘图

Question

I am attempting to do some very simple 2D drawing with GLKit, including using a texture. However, if I load the texture, but don't even use it in the drawing, somehow it prevents the drawing from taking place!

Here is my setup code:

-(void) setup {

  effect = [[GLKBaseEffect alloc] init];

  // comment this out - drawing takes place
  texture = [GLKTextureLoader textureWithCGImage:[UIImage imageNamed: @"arrow.png"].CGImage options:nil error: nil];
  if (texture) {
    effect.texture2d0.envMode = GLKTextureEnvModeReplace;
    effect.texture2d0.target = GLKTextureTarget2D;
    effect.texture2d0.name = texture.name;
  };
  // end of comment this out...

  effect.transform.projectionMatrix = GLKMatrix4MakeOrtho(0.0, self.bounds.size.width, self.bounds.size.height, 0.0, 1, -1);

}

Here is my drawing code:

- (void)drawRect:(CGRect)rect {

  GLKVector2 vertices[4];
  GLKVector4 colors[4];

  vertices[0] = GLKVector2Make(20.0, 30.0);
  vertices[1] = GLKVector2Make(120.0, 45.0);
  vertices[2] = GLKVector2Make(70.0, 88.0);
  vertices[3] = GLKVector2Make(20.0, 80.0);

  for(int i = 0; i < 4; i++) {

    colors[i] = GLKVector4Make(0.3, 0.8, 0.5, 1.0);
  };

  glClearColor(0.85, 0.05, 0.1, 1.0);
  glClear(GL_COLOR_BUFFER_BIT);

  [effect prepareToDraw];

  glEnable(GL_BLEND);
  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

  glEnableVertexAttribArray(GLKVertexAttribPosition);
  glEnableVertexAttribArray(GLKVertexAttribColor);

  glVertexAttribPointer(GLKVertexAttribPosition, 2, GL_FLOAT, GL_FALSE, 0, vertices);
  glVertexAttribPointer(GLKVertexAttribColor, 4, GL_FLOAT, GL_FALSE, 0, colors);

  glDrawArrays(GL_TRIANGLE_STRIP, 0, 3);


  glDisableVertexAttribArray(GLKVertexAttribPosition);
  glDisableVertexAttribArray(GLKVertexAttribColor);

  glDisable(GL_BLEND);
}

Answer 1

For debugging OpenGL, run the code in Debug mode, then pause it and choose "Capture OpenGL ES frame" from the menu bar. This allows you to step through your drawing code and see the OpenGL state after each call. Therefore, you can compare the states between when you do the setup code and when you don't do it, and can pin down the bug.

For the problem itself: Setting the texture2d property of the effect is already enough to use the texture. It is automatically used in the drawing if you put it there. In [effect prepareToDraw] , the whole state of the effect is applied - including the specified texture.