Using GL_TEXTURE_2D_ARRAY as a draw target

Question

I've created an array of 2D textures and initialized it with glTexImage3D. Then I attached separate textures to color attachments with glFramebufferTextureLayer, Framebuffer creation doesn't throw an error and everything seems fine until the draw call happens.

When shader tries to access color attachment the following message appears:

OpenGL Debug Output message : Source : API; Type : ERROR; Severity : HIGH;
GL_INVALID_OPERATION error generated. <location> is invalid.

Shaders are accessing layers of an array with location qualifier:

layout (location = 0) out vec3 WorldPosOut; 
layout (location = 1) out vec3 DiffuseOut; 
layout (location = 2) out vec3 NormalOut; 
layout (location = 3) out vec3 TexCoordOut; 

Documentation says that glFramebufferTextureLayer works just like glFramebufferTexture2D, except the layer parameter, so can I use location qualifiers with texture array, or some other way exsists?

Answer 1

I finally managed to bind texture array as a color buffer. It is hard to find useful information on the topic, so here is an instruction:

№1. You need to create a texture array and initialize it properly:

glGenTextures(1, &arrayBuffer);
glBindTexture(GL_TEXTURE_2D_ARRAY, arrayBuffer);

// we should initialize layers for each mipmap level
    for (int mip = 0; mip < mipLevelCount; ++mip) {

glTexImage3D(GL_TEXTURE_2D_ARRAY, mip, internalFormat, ImageWidth, ImageHeight,
 layerCount, 0, GL_RGB, GL_UNSIGNED_INT, 0);
glTexParameterf(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MIN_FILTER, textureFilter);
glTexParameterf(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MAG_FILTER, textureFilter);
glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_BASE_LEVEL, 0);
glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MAX_LEVEL, mipLevelCount - 1);
glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

}

Keep in mind, that setting texture parameters like MIN/MAG filters and BASE/MAX mipmap level is important. OpenGL sets maximum mipmap level to 1000 and if you didn't provide the whole thousand of mipmaps you will get an incomplete texture, you won't get anything except the black screen.

№2. Don't forget to bind arrayBuffer to the GL_TEXTURE_2D_ARRAY target before attaching the layers to the color buffers:

glBindTexture(GL_TEXTURE_2D_ARRAY, arrayBuffer);

for (unsigned int i = 0; i < NUMBER_OF_TEXTURES; i++) {

glFramebufferTextureLayer(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + i, arrayBuffer, 0, i);

}

Don't forget to set the GL_TEXTURE_2D_ARRAY target to 0 with glBindTexture or it can get modified outside of the initialization code.

№3. Since the internalFormat of each image in the array must stay the same, I recommend to create a separate texture for the depth/stencil buffer:

glGenTextures(1, &m_depthTexture);

...

glBindTexture(GL_TEXTURE_2D, m_depthTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH32F_STENCIL8, WindowWidth,
WindowHeight, 0, GL_DEPTH_STENCIL, GL_FLOAT_32_UNSIGNED_INT_24_8_REV, NULL);

glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 0);

glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT,
GL_TEXTURE_2D, m_depthTexture, 0);

Don't forget to set up index for each color buffer:

for (int i = 0; i < GBUFFER_NUM_TEXTURES; ++i)
        DrawBuffers[i] = GL_COLOR_ATTACHMENT0 + i; //Sets appropriate indices for each color buffer

glDrawBuffers(ARRAY_SIZE_IN_ELEMENTS(DrawBuffers), DrawBuffers);

In shaders you can use layout(location = n) qualifiers to specify the color buffer.

OpenGL 3 Note (NVIDIA): glFramebufferTextureLayer is available since OpenGL 3.2 (Core profile), but on NVIDIA GPU's drivers will force OpenGL version to 4.5, so you should specify the exact version of OpenGL if you care about compatibility. I use SDL2 in my application, so I use the following calls to set OpenGL version:

SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);

Results of the deferred shading: