CODEWITHSUNDEEP
c++opengltexturestexture2d
Luca
Luca

Reputation: 11016

OpenGL PBO and texture objects: Do I need to allocate memory for both

I am using a pixel buffer object and texture as follows:

// Initialize PBO
Gluint _buffer;
Glenum target = GL_PIXEL_UNPACK_BUFFER
glGenBuffers(1, &_buffer);
if (_buffer) {
    glBindBuffer(target, _buffer);
    glBufferData(target, rows * cols * 4, NULL, GL_DYNAMIC_COPY);
    glBindBuffer(target, 0);
}

Now I load the data into the PBO as follows:

glBindBuffer(target, _buffer);
GLubyte * data = (GLubyte *)glMapBuffer(target, GL_READ_WRITE);
memcpy(data, my_image_data, rows * cols * 4);
glUnmapBuffer(target);
glBindBuffer(target, 0);

My question is when I map this PBO to a texture, do I need to allocate memory for the texture as well (essentially doing a copy). Or can I simply map it without any allocation of memory.

// Without allocation of texture memory
GLuint t;
glBindBuffer(target, t);
glGenTextures(1, &t);
glBindTexture(GL_TEXTURE_2D, t);
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, _cols, _rows,
                    GL_BGRA, GL_UNSIGNED_BYTE, NULL);
glBindTexture(GL_TEXTURE_2D, 0);
glBindBuffer(target, 0);

Or should I also have the memory allocation of the texture. So a call like:

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, cols, rows, 0, GL_BGRA, 
             GL_UNSIGNED_BYTE, (GLvoid *)NULL);

after glBindTexture().

Upvotes: 0

Views: 664

Answers (2)

datenwolf
datenwolf

Reputation: 162317

In short, yes you have to allocate textures individually. Unfortunately in OpenGL it is not possible to bind an existing memory region to a texture sampler and use it like that. There have been multiple attempts in getting it into OpenGL (superbuffers and the likes, around 2004).

The ability to use the same memory region with different functional units is one of the big things people are eager for with the Vulkan API.

Upvotes: 1

peppe
peppe

Reputation: 22826

Yes, you must allocate storage (via glTexStorage or glTexImage or glCopyTexImage etc.) before being able to upload texture data into an image.

If you attempt to use glTexSubImage2D on a texture without allocated storage it will fail.

Upvotes: 3

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