GLAPI/glGetTexImage

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glGetTexImage
Core in version 4.4
Core since version 1.0

glGetTexImage: return a texture image

Function Definition

 void glGetTexImage(GLenum target​, GLint level​, GLenum format​, GLenum type​, GLvoid * img​);
target
Specifies which texture is to be obtained. GL_TEXTURE_1D​, GL_TEXTURE_2D​, GL_TEXTURE_3D​, GL_TEXTURE_1D_ARRAY​, GL_TEXTURE_2D_ARRAY​, GL_TEXTURE_RECTANGLE​, GL_TEXTURE_CUBE_MAP_POSITIVE_X​, GL_TEXTURE_CUBE_MAP_NEGATIVE_X​, GL_TEXTURE_CUBE_MAP_POSITIVE_Y​, GL_TEXTURE_CUBE_MAP_NEGATIVE_Y​, GL_TEXTURE_CUBE_MAP_POSITIVE_Z​, and GL_TEXTURE_CUBE_MAP_NEGATIVE_Z​ are accepted.
level
Specifies the level-of-detail number of the desired image. Level 0 is the base image level. Level n is the nth mipmap reduction image.
format
Specifies a pixel format for the returned data. The supported formats are GL_STENCIL_INDEX​, GL_DEPTH_COMPONENT​, GL_DEPTH_STENCIL​, GL_RED​, GL_GREEN​, GL_BLUE​, GL_RG​, GL_RGB​, GL_RGBA​, GL_BGR​, GL_BGRA​, GL_RED_INTEGER​, GL_GREEN_INTEGER​, GL_BLUE_INTEGER​, GL_RG_INTEGER​, GL_RGB_INTEGER​, GL_RGBA_INTEGER​, GL_BGR_INTEGER​, GL_BGRA_INTEGER​.
type
Specifies a pixel type for the returned data. The supported types are GL_UNSIGNED_BYTE​, GL_BYTE​, GL_UNSIGNED_SHORT​, GL_SHORT​, GL_UNSIGNED_INT​, GL_INT​, GL_HALF_FLOAT​, GL_FLOAT​, 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​, GL_UNSIGNED_INT_24_8​, GL_UNSIGNED_INT_10F_11F_11F_REV​, GL_UNSIGNED_INT_5_9_9_9_REV​, and GL_FLOAT_32_UNSIGNED_INT_24_8_REV​.
img
Returns the texture image. Should be a pointer to an array of the type specified by type​.

Description

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​.

Notes

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_STENCIL_INDEX​ is accepted for format​ only if the GL version is 4.4 or greater.

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 log2(max), where max is the returned value of GL_MAX_TEXTURE_SIZE​.

GL_INVALID_OPERATION​ is generated 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 generated 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 format​ is GL_STENCIL_INDEX​ and the base internal format is not GL_STENCIL_INDEX​ or GL_DEPTH_STENCIL​.

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​.

Associated Gets

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​

See Also

glActiveTexture, glBindTexture, glPixelStore, glReadPixels, glTexSubImage1D, glTexSubImage2D, glTexSubImage3D

Copyright

Copyright © 1991-2006 Silicon Graphics, Inc. Copyright © 2010-2013 Khronos Group. This document is licensed under the SGI Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.