glCopyTexImage2D

glCopyTexImage2D: man3/glCopyTexImage2D.xml

glCopyTexImage2D defines a two-dimensional texture image, or cube-map texture image with pixels from the current GL_READ_BUFFER. The screen-aligned pixel rectangle with lower left corner at ( x, y ) and with a width of width and a height of height defines the texture array at the mipmap level specified by level. internalformat specifies the internal format of the texture array. The pixels in the rectangle are processed exactly as if glReadPixels had been called, but the process stops just before final conversion. At this point all pixel component values are clamped to the range 0 1 and then converted to the texture's internal format for storage in the texel array. Pixel ordering is such that lower x and y screen coordinates correspond to lower s and t texture coordinates. If any of the pixels within the specified rectangle of the current GL_READ_BUFFER are outside the window associated with the current rendering context, then the values obtained for those pixels are undefined. When internalformat is one of the sRGB types, the GL does not automatically convert the source pixels to the sRGB color space. In this case, the glPixelMap function can be used to accomplish the conversion.

1, 2, 3, and 4 are not accepted values for internalformat. An image with height or width of 0 indicates a null texture.