OpenGL ES 2.0 & the Depth Buffer/Texture
I’m currently in the process of implementing shadow mapping for my OpenGL app and ran across this depth buffer issue – according to the OpenGL ES 2.0 specs (both PowerVR and http://developer.meego.com/api/1.2/opengles-2.0/glTexImage2D.html), a texture format GL_DEPTH_COMPONENT is not supported. However I tried and it does compile for Harmattan. Didn’t yet run it to see whether there is an error. Any experiences on this? I really dislike the idea of having to pack the depth values into a RGBA texture.
- Matti
6 replies
Does PowerVR support this extension? http://www.khronos.org/registry/gles/extensions/OES/OES_depth_texture.txt
It would appear that the SGX 530, at least, does not.
http://www.rojtberg.net/348/powervr-sgx-530-does-not-support-depth-textures/
Which would be sad since the performance I’m getting out of a RGBA packed depth texture is not very good. I’ll check with glGetString() later. The most modern phones seem to support the extension (ref google) so I guess it’s worth implementing even if mine doesnt .)
Well, the device seems to have extensions GL_OES_depth_texture, GL_OES_depth24, GL_OES_texture_float etc. which would hint that this should work. However if I try to pass GL_DEPTH_COMPONENT as the format, glTexImage2D() fails – well, this is what the OpenGL ES 2.0 spec does say, after all, GL_DEPTH_COMPONENT is not among the supported choices.
I tried creating a RGBA texture and was able to attach it to a FBO as GL_DEPTH_ATTACHMENT using glFramebufferTexture2D() and everything goes fine on paper. Rendering / reading that texture doesnt really work like with a depth texture (which I have working on the desktop build very nicely).
Such a shame.
See kids, this is what happens when you don’t read the documentation :) Changing the <type> parameter to GL_UNSIGNED_INT did the trick. I’ll share the code so maybe the next guy is spared the hassle:
Creating the FBO:
- bool GLController::CreateDepthTextureAndFBO(GLuint* fboId,
- GLuint* depthTextureId,
- GLuint* renderBuffer,
- int width, int height)
- {
- // Create a framebuffer object
- glGenFramebuffers(1, fboId);
- glBindFramebuffer(GL_FRAMEBUFFER, *fboId);
- // Create a render buffer
- glGenRenderbuffers(1, renderBuffer);
- glBindRenderbuffer(GL_RENDERBUFFER, *renderBuffer);
- // Create a texture for storing the depth
- glGenTextures(1, depthTextureId);
- glBindTexture(GL_TEXTURE_2D, *depthTextureId);
- glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
- glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
- // Remove artifact on the edges of the shadowmap
- glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
- glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
- Debug("glGetError() 0 = 0x%x", glGetError());
- if ( m_hasDepthTextureExtension )
- {
- // We'll use a depth texture to store the depths in the shadow map
- glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, width, height, 0,
- GL_DEPTH_COMPONENT, GL_UNSIGNED_INT, NULL);
- // Attach the depth texture to FBO depth attachment point
- glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,
- GL_TEXTURE_2D, *depthTextureId, 0);
- }
- else
- {
- // We'll use a RGBA texture into which we pack the depth info
- glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0,
- GL_RGBA, GL_UNSIGNED_BYTE, NULL);
- // Attach the RGBA texture to FBO color attachment point
- glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
- GL_TEXTURE_2D, *depthTextureId, 0);
- // Allocate 16-bit depth buffer
- glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, width, height);
- // Attach the render buffer as depth buffer - will be ignored
- glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,
- GL_RENDERBUFFER, *renderBuffer);
- }
- // check FBO status
- GLenum fboStatus = glCheckFramebufferStatus(GL_FRAMEBUFFER);
- if ( fboStatus != GL_FRAMEBUFFER_COMPLETE )
- {
- Debug("FBO not complete: 0x%x", fboStatus);
- return false;
- }
- // Go back to using the default frame buffer
- glBindFramebuffer(GL_FRAMEBUFFER, DefaultFramebufferId);
- return true;
- }
Shaders for rendering the depth:
- const char* DepthShadowMapVertexShader =
- GLSL_VERSION_STRING \
- "precision highp float;\n" \
- "\n" \
- "attribute vec3 in_coord;\n" \
- "uniform mat4 mvp_matrix;\n" \
- "\n" \
- "void main()\n" \
- "{\n" \
- " gl_Position = mvp_matrix * vec4(in_coord, 1.0);\n" \
- "}\n";
- const char* DepthShadowMapFragmentShader =
- GLSL_VERSION_STRING \
- "precision highp float;\n" \
- "\n" \
- "void main()\n" \
- "{\n" \
- "}\n";
Shaders using the shadow map: see http://fabiensanglard.net/shadowmapping/index.php#c5t_form
Cheers to Fabian Sanglard +others for help and ideas on this issue.
- Matti
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