GLSL - Unpack in a SSB (V2) - c++

Question

This question continue the subject here : Unpack in a SSB
With the previous setup, I found myself incapable to reset my SSB using the Pixel Unpack buffer.
My init function :
//Storage Shader buffer
glGenBuffers(1, &m_buffer);
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, m_buffer);
glBufferData(
GL_SHADER_STORAGE_BUFFER,
1 * sizeof(uint),
NULL,
GL_DYNAMIC_DRAW);
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, 0);
//Texture
glGenTextures(1, &m_texture);
glBindTexture(GL_TEXTURE_2D, m_texture);
glTexStorage2D(GL_TEXTURE_2D, 1, GL_R32UI, 1, 1);
glTexBufferRange(
GL_TEXTURE_BUFFER,
GL_R32UI,
m_buffer,
0,
1 * 1 * sizeof(GLuint));
glBindTexture(GL_TEXTURE_2D, 0);
//Unpack buffer
uint clearData = 5;
glGenBuffers(1, &m_clearBuffer);
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, m_clearBuffer);
glBufferData(
GL_PIXEL_UNPACK_BUFFER,
1 * 1 * sizeof(GLuint),
&clearData,
GL_STATIC_COPY);
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
My clearing function
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, m_clearBuffer);
glBindTexture(GL_TEXTURE_2D, m_texture);
glTexSubImage2D(
GL_TEXTURE_2D,
0,
0,
0,
1,
1,
GL_RED_INTEGER,
GL_UNSIGNED_INT,
NULL);
glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
glBindTexture(GL_TEXTURE_2D, 0);
The clear function doesn't work. If I try to access the value in the buffer with glBufferSubData(), BAADF00D is returned. If instead of an upack operation I use a simple glBufferSubData() It works.
How do I reset properly my SSB with the Pixel Unpack buffer ?
ANSWER :
The problem was binding my texture to GL_TEXTURE_2D instead of GL_TEXTURE_BUFFER. However, there is an easier way to unpack inside my SSB :
m_pFunctions->glBindBuffer(GL_PIXEL_UNPACK_BUFFER, m_clearBuffer);
m_pFunctions->glBindBuffer(GL_ARRAY_BUFFER, m_buffer);
m_pFunctions->glCopyBufferSubData(
GL_PIXEL_UNPACK_BUFFER,
GL_ARRAY_BUFFER,
0,
0,
1);
m_pFunctions->glBindBuffer(GL_ARRAY_BUFFER, 0);
m_pFunctions->glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);
This way I don't even need a texture.

Answer 1

You are using texture buffer objects incorrectly. You are creating an ordinary 2D texture (including the actual storage) and then seem to try define a buffer of the storage. Your glTexBufferRange() call will fail since you don't have any texture object bound to the GL_TEXTURE_BUFFER target.
But simply binding m_texture there will not make sense either. The point of TBOs is to make a buffer object available as a texture. You can not modify the TBO contents via the texture paths, glTex(Sub)Image/glTexStorage are not allowed for buffer textures, you have to use the buffer update mechanisms.
I don't see why you even try to do it via the texture path. Modyfing the underlying data storage is enough. And you can simply copy the contents of your PBO (or whatever kind of buffer you want to use) over to the buffer defining the storage for your TBO via glCopyBufferSubData(). Or, with modern GL, the most efficient approach might be using glClearBufferData directly on the SSBO.