HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 218

G glGetTexImage If the selected texture image does not contain four components, the following mappings are applied. Single-component textures are treated as RGBA buffers with red set to the single-component value, green set to 0, blue set to 0, and alpha set to 1. Two-component textures are treated as RGBA buffers with red set to the value of component zero, alpha set to the value of component one, and green and blue set to 0. Finally, three-component textures are treated as RGBA buffers with red set to component zero, green set to component one, blue set to component two, and alpha set to 1. To determine the required size of pixels, use glGetTexLevelParameter to determine the dimensions of the internal texture image, then scale the required number of pixels by the storage required for each pixel, based on format and type. Be sure to take the pixel storage parameters into account, especially GL_PACK_ALIGNMENT. Notes If an error is generated, no change is made to the contents of pixels. Errors • GL_INVALID_ENUM is generated if target, format, or type is not an accepted value. • GL_INVALID_VALUE is generated if level is less than 0. • GL_INVALID_VALUE may be generated if level is greater than $log sub 2 max$, where $max$ is the returned value of GL_MAX_TEXTURE_SIZE. • GL_INVALID_OPERATION is generated if glGetTexImage is executed between the execution of glBegin and the corresponding execution of glEnd. Associated Gets glGetTexLevelParameter with argument GL_TEXTURE_WIDTH glGetTexLevelParameter with argument GL_TEXTURE_HEIGHT glGetTexLevelParameter with argument GL_TEXTURE_BORDER glGetTexLevelParameter with argument GL_TEXTURE_COMPONENTS glGet with arguments GL_PACK_ALIGNMENT and others See Also glDrawPixels, glReadPixels, glTexEnv, glTexGen, glTexImage1D, glTexImage2D, glTexSubImage1D, glTexSubImage2D, glTexParameter 218 Chapter 7