glGetTexImage

glGetTexImage: man2/glGetTexImage.xml

glGetTexImage returns a texture image into img. target specifies whether the desired texture image is one specified by glTexImage1D ( GL_TEXTURE_1D ), glTexImage2D ( GL_TEXTURE_2D or any of GL_TEXTURE_CUBE_MAP_* ), or glTexImage3D ( GL_TEXTURE_3D ). level specifies the level-of-detail number of the desired image. format and type specify the format and type of the desired image array. See the reference pages glTexImage1D and glDrawPixels for a description of the acceptable values for the format and type parameters, respectively. If a non-zero named buffer object is bound to the GL_PIXEL_PACK_BUFFER target (see glBindBuffer ) while a texture image is requested, img is treated as a byte offset into the buffer object's data store. To understand the operation of glGetTexImage, consider the selected internal four-component texture image to be an RGBA color buffer the size of the image. The semantics of glGetTexImage are then identical to those of glReadPixels, with the exception that no pixel transfer operations are performed, when called with the same format and type, with and set to 0, set to the width of the texture image (including border if one was specified), and set to 1 for 1D images, or to the height of the texture image (including border if one was specified) for 2D images. Because the internal texture image is an RGBA image, pixel formats GL_COLOR_INDEX, GL_STENCIL_INDEX, and GL_DEPTH_COMPONENT are not accepted, and pixel type GL_BITMAP is not accepted. 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 img, 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.

If an error is generated, no change is made to the contents of img. The types GL_UNSIGNED_BYTE_3_3_2, GL_UNSIGNED_BYTE_2_3_3_REV, GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV, GL_UNSIGNED_SHORT_4_4_4_4, GL_UNSIGNED_SHORT_4_4_4_4_REV, GL_UNSIGNED_SHORT_5_5_5_1, GL_UNSIGNED_SHORT_1_5_5_5_REV, GL_UNSIGNED_INT_8_8_8_8, GL_UNSIGNED_INT_8_8_8_8_REV, GL_UNSIGNED_INT_10_10_10_2, GL_UNSIGNED_INT_2_10_10_10_REV, and the formats GL_BGR, and GL_BGRA are available only if the GL version is 1.2 or greater. For OpenGL versions 1.3 and greater, or when the ARB_multitexture extension is supported, glGetTexImage returns the texture image for the active texture unit.