GlGetTexImage

_glGetTexImage: return a texture image

Syntax

 SUB _glGetTexImage (BYVAL target AS _UNSIGNED LONG, BYVAL level AS LONG, BYVAL format AS _UNSIGNED LONG, BYVAL type AS _UNSIGNED LONG, pixels AS _OFFSET)
 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.

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</sub>(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.

Use With:

_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