glGetTexImage - return a texture image
void glGetTexImage(GLenum target, GLint level, GLenum format, GLenum type, GLvoid * img);
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_1D_ARRAY, GL_TEXTURE_RECTANGLE, GL_TEXTURE_2D or any of GL_TEXTURE_CUBE_MAP_*), or glTexImage3D() (GL_TEXTURE_2D_ARRAY, 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 page for glTexImage1D() 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 x and y set to 0, width set to the width of the texture image and height set to 1 for 1D images, or to the height of the texture image for 2D images.
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.
glGetTexImage returns the texture image for the active texture unit.
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 2 max, where max is the returned value of GL_MAX_TEXTURE_SIZE.
GL_INVALID_OPERATION is returned if type is one of 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, or GL_UNSIGNED_INT_10F_11F_11F_REV and format is not GL_RGB.
GL_INVALID_OPERATION is returned if type is one of 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, or GL_UNSIGNED_INT_5_9_9_9_REV and format is neither GL_RGBA or GL_BGRA.
GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to the GL_PIXEL_PACK_BUFFER target and the buffer object's data store is currently mapped.
GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to the GL_PIXEL_PACK_BUFFER target and the data would be packed to the buffer object such that the memory writes required would exceed the data store size.
GL_INVALID_OPERATION is generated if a non-zero buffer object name is bound to the GL_PIXEL_PACK_BUFFER target and img is not evenly divisible into the number of bytes needed to store in memory a datum indicated by type.
glGetTexLevelParameter() with argument GL_TEXTURE_WIDTH
glGetTexLevelParameter() with argument GL_TEXTURE_HEIGHT
glGetTexLevelParameter() with argument GL_TEXTURE_INTERNAL_FORMAT
glGet() with arguments GL_PACK_ALIGNMENT and others
glGet() with argument GL_PIXEL_PACK_BUFFER_BINDING
glActiveTexture(), glReadPixels(), glTexImage1D(), glTexImage2D(), glTexImage3D(), glTexSubImage1D(), glTexSubImage2D(), glTexSubImage3D(), glTexParameter()
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