Deferred shading in OpenGL?

Question

I've got a strange problem with my deferred shading implementation. I render the required information via MRT into a FBO, currently diffuse, position and normals in world space, which looks like this:

enter image description here

This is done with the following setup for all tree textures:

diffuse = std::shared_ptr<bb::Texture>(new bb::Texture(GL_TEXTURE_2D)); // generates texture ID diffuse->bind(); diffuse->texture2D(0, GL_RGB, width, height, 0, GL_RGB, GL_FLOAT, 0); // glTexture2D diffuse->parameterf(GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); diffuse->parameterf(GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); diffuse->parameterf(GL_TEXTURE_MIN_FILTER, GL_LINEAR); diffuse->parameterf(GL_TEXTURE_MAG_FILTER, GL_LINEAR); diffuse->unbind(); texture2D(GL_COLOR_ATTACHMENT0+1, diffuse->getID(), 0);

These are then used in my drawing stage:

dsShader->bind(); dsShader->enableVertexAttribArrays(); ds->diffuse->bind(GL_TEXTURE0); // "ds" is an FBO containing the textures ds->position->bind(GL_TEXTURE0+1); ds->normal->bind(GL_TEXTURE0+2); dsShader->sendUniform("diffuse", 0); dsShader->sendUniform("position", 1); dsShader->sendUniform("normal", 2); dsShader->sendUniform("camera", camera3D->position.x, camera3D->position.y, camera3D->position.z); dsOut->indexBuffer->bind(); dsOut->vertex2Buffer->bind(); dsOut->vertex2Buffer->vertexAttribPointer(dsShader->getAttribLocation("vertex0"), 2, GL_FLOAT, false, 0, 0); glDrawElements(GL_TRIANGLES, dsOut->indexBuffer->size(), GL_UNSIGNED_INT, 0); ds->diffuse->unbind(); ds->position->unbind(); ds->normal->unbind(); dsShader->disableVertexAttribArrays(); dsShader->unbind();

With the following shader (just the necessary part, the light source is hardcoded):

struct DirLight{ vec3 direction; vec4 diffuse, specular; }; uniform sampler2D diffuse; uniform sampler2D position; uniform sampler2D normal; uniform vec3 camera; DirLight light0 = DirLight(vec3(1, 1, 0), vec4(0.3), vec4(0.1)); in vec2 vertex; void main(){ vec4 color = texture(diffuse, vertex)*0.5; vec3 p = vec3(texture(position, vertex)); vec3 n = normalize(vec3(texture(normal, vertex))); float ndotl = max(dot(n, normalize(light0.direction)), 0.0); // simple phong if(ndotl > 0.0){ color += ndotl*light0.diffuse; } gl_FragColor = color; }

The wierd part is, if I set the light source direction to negative values, lets say:

DirLight light0 = DirLight(vec3(-1, 0, 0), vec4(0.3), vec4(0.1));

The final result is not shaded. It looks right for positive values (more or less). Here is a picture of the output:

enter image description here

And there could also be a problem with the normals, marked in the red area.

It sounds like a problem with your normals. Have you tried rendering the scene, without deferred shading? — Gurgadurgen
– Gurgadurgen, Commented Apr 6, 2014 at 13:06
Yep I tried that, no problem. You can see the output of all tree textures in the first picture. Something I forgot to mention is that my z-axis is the upper axis. — Kugel
– Kugel, Commented Apr 6, 2014 at 13:21
It looks like your normals are reversed, in the first one. I would suggest trying to fix that, first, then coming back and testing the negative values, again. — Gurgadurgen
– Gurgadurgen, Commented Apr 6, 2014 at 14:05
What is the format of your normal G-Buffer? In your attached screenshot, you have neglected to scale and bias the normals into the visible color range... that is to say, any normal that has a negative value is clipped by GL when displayed on the default framebuffer simply to black. If you are trying to store the normals in a format like GL_RGB then the G-Buffer itself also has this behavior. You can either use something like GL_RGB8_SNORM or do the old * 0.5 + 0.5 to manually scale into [0,1] and * 2.0 - 1.0 trick to scale back to [-1,1]. — Andon M. Coleman
– Andon M. Coleman, Commented Apr 7, 2014 at 15:33
@AndonM.Coleman Your solution seems to have worked for the OP. You should consider posting it as an answer. — Jason C
– Jason C, Commented Apr 9, 2014 at 16:31

Kugel · Accepted Answer · 2014-04-09 15:27:52Z

2

Ok the solution by Andon M. Coleman works, I switched the internal format to GL_RGB8_SNORM. Thanks for your help :)

answered Apr 9, 2014 at 15:27

Kugel

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1 Comment

Jason C Over a year ago

Since this appeared in the flag review queue, here is a note for reviewers: This actually is an answer, not a "thank you". There are no other answers currently posted for this question. The answer was suggested in question comments and the OP has helpfully summarized it here. @user3476897: Suggest accepting Andon's answer if he decides to post an answer.

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