How to get texture data using textureID's in openGL

Question

I\'m writing some code where all I have access to is a textureID to get access to the required texture. Is there any way that I can get access to the RGB values of this text

Answer 1

You are probably looking for glGetTexImage (see https://www.khronos.org/opengl/wiki/GLAPI/glGetTexImage for further information).

Before using glGetTexImage, don't forget to use glBindTexture (https://www.khronos.org/opengl/wiki/GLAPI/glBindTexture) with your texture ID.

Answer 2

In OpneGL a texture can be read by glGetTexImage/glGetnTexImage respectively the DSA version of the function glGetTextureImage.

Another possibility is to attach the texture to a framebuffer and to read the pixel by glReadPixels. OpenGL ES does not offer a glGetTexImage, so this is the way to OpenGL ES.
See opengl es 2.0 android c++ glGetTexImage alternative

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If you transfer the texture image to a Pixel Buffer Object, then you can even access the data via Buffer object mapping. See also OpenGL Pixel Buffer Object (PBO).
You've to bind a buffer with the proper size to the target GL_PIXEL_PACK_BUFFER:

// create buffer
GLuint pbo;
glGenBuffers(1, &pbo);
glBindBuffer(GL_PIXEL_PACK_BUFFER, pbo);
glBufferData(GL_PIXEL_PACK_BUFFER, size_in_bytes, 0, GL_STATIC_READ);

// get texture image
glBindTexture(GL_TEXTURE_2D, texture_obj);
glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA, GL_UNSIGNED_BYTE, (void*)(0));

// map pixel buffer
void * data_ptr = glMapBuffer(GL_PIXEL_PACK_BUFFER, GL_READ_ONLY);

// access the data
// [...]

glUnmapBuffer(GL_PIXEL_PACK_BUFFER);