OpenGL ES Depth Buffer rendering (iOS simulator VS real device)

Question

When rendering the depth buffer with the iOS simulator Getting the true z value from the depth buffer , all is fine. But the rendering on real device gives bad result: the depth is rendered with only few values (there is no fade) like when you display an image into a 256 values color range.

Here is the code for the fbo generation:

glGenFramebuffers(1, &sceneFBO);
glGenTextures(2, textures_scene);
glBindTexture(GL_TEXTURE_2D, textures_scene[0]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, widthResolution, heightResolution, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

glBindTexture(GL_TEXTURE_2D, textures_scene[1]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, widthResolution, heightResolution, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_INT, NULL);

//TODO: GL_DEPTH_COMPONENT cannot be GL_UNSIGNED_BYTE ?

glBindFramebuffer(GL_FRAMEBUFFER, sceneFBO);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, textures_scene[0], 0);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, textures_scene[1], 0);

It seems that the only working value for GL_DEPTH_ATTACHMENT fbo is GL_UNSIGNED_INT. But it is not enough to render the depth...

PS: I don't want to display again the scene into a GL_COLOR_ATTACHMENT0 with the z-values in order to have a correct depth (for performance reasons) nor use OpenGL ES3.0 or the new metal (iPhone4s support).

Any idea?

Answer 1

ES 1或2不支持深度缓冲区。请参见以下问题的答案： glReadPixels无法在iOS上读取深度缓冲区值

Answer 2

似乎无法使用GL_UNSIGNED_BYTE作为类型参数以及GL_DEPTH_COMPONENT作为内部 GL_OES_depth_texture根据GL_OES_depth_texture扩展规范，仅允许GL_UNSIGNED_SHORT和GL_UNSIGNED_INT ： https : GL_OES_depth_texture 。文本

Answer 3

I finally put the z value in the alpha part of the scene (I don't use transparency for this fbo).

 color.w=(gl_postion.z-near)/(far-near)

A little mcgyver but it does the job.