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169 lines
5.5 KiB
Plaintext
169 lines
5.5 KiB
Plaintext
Name
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ANGLE_pack_reverse_row_order
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Name Strings
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GL_ANGLE_pack_reverse_row_order
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Contact
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Daniel Koch, TransGaming (daniel 'at' transgaming.com)
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Contributors
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Brian Salomon
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Daniel Koch
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Status
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Implemented in ANGLE ES2
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Version
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Last Modified Date: February 22, 2011
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Author Revision: 22
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Number
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OpenGL ES Extension #110
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Dependencies
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OpenGL 1.5 or OpenGL ES 1.0 are required.
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Some of the functionality of this extension is not supported
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when implemented against OpenGL ES.
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EXT_texture_rg interacts with this extension.
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The extension is written against the OpenGL 3.2 Specification
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(Core Profile).
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Overview
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This extension introduces a mechanism to allow reversing the order
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in which image rows are written into a pack destination. This
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effectively allows an application to flip the results of a ReadPixels
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in the y direction operation without having to render upside down.
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The coordinate system of OpenGL is vertically reversed in comparison to a
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number of other graphics systems such as native windowing APIs. Applications
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that perform ReadPixels may have to either render to an intermediate color
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buffer before calling ReadPixels or perform a flip in software after
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ReadPixels. In some systems the GL can perform the row reversal during
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ReadPixels without incurring additional cost.
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IP Status
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No known IP claims.
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New Procedures and Functions
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None
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New Types
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None
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New Tokens
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Accepted by the <pname> parameter of PixelStore{if}, GetIntegerv(),
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GetBooleanv(), and GetFloatv():
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PACK_REVERSE_ROW_ORDER_ANGLE 0x93A4
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Additions to Chapter 3 of the OpenGL 3.2 Specification (Rasterization)
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In Section 4.3.1 (Reading Pixels) add a row to table 4.7:
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+------------------------------+---------+---------------+-------------+
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| Parameter Name | Type | Initial Value | Valid Range |
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+------------------------------+---------+---------------+-------------+
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| PACK_REVERSE_ROW_ORDER_ANGLE | boolean | FALSE | TRUE/FALSE |
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+------------------------------+---------+---------------+-------------+
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In Section 4.3.1 (Reading Pixels) modify the second paragraph of subsection
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"Placement in Pixel Pack Buffer or Client Memory" to read:
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When PACK_REVERSE_ROW_ORDER_ANGLE is FALSE groups of elements are placed
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in memory just as they are taken from memory when transferring pixel
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rectangles to the GL. That is, the ith group of the jth row
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(corresponding to the ith pixel in the jth row) is placed in memory just
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where the ith group of the jth row would be taken from when transferring
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pixels. See Unpacking under section 3.7.2. The only difference is that
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the storage mode parameters whose names begin with PACK_ are used
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instead of those whose names begin with UNPACK_. If the format is RED,
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GREEN, BLUE, or ALPHA, only the corresponding single element is written.
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Likewise if the format is RG, RGB, or BGR, only the corresponding two or
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three elements are written. Otherwise all the elements of each group are
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written. When PACK_REVERSE_ROW_ORDER_ANGLE is TRUE the order of the rows
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of elements is reversed before the data is packed. That is, the element
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corresponding to pixel (x, y + height - 1) becomes the first element
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packed, followed by (x + 1, y + height - 1), etc. Otherwise, pixel data
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is packed in the same manner as when PACK_REVERSE_ROW_ORDER_ANGLE is
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FALSE.
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Additions to Chapter 6 of the OpenGL 3.2 Specification (State and State Requests)
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In Section 6.1.4 add the following sentence to the fifth paragraph
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(beginning with "For three-dimensional and two-dimensional array
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textures..."):
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When PACK_REVERSE_ROW_ORDER_ANGLE is TRUE the order of rows within
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each image are reversed without reordering the images themselves.
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Dependencies on OpenGL ES
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If implemented for OpenGL ES, this extension behaves as specified, except:
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-Delete all references to formats RED, GREEN, BLUE, RG, and BGR.
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-The language about image order in Section 6.1.4 does not apply as OpenGL ES
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does not have GetTexImage.
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Dependencies on EXT_texture_rg
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If EXT_texture_rg is present reinsert language about formats RED and RG
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into the OpenGL ES 2.0 specification.
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Errors
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None
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New State
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Initial
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Get Value Type Get Command Value Description Sec.
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--------- ---- ----------- ------- ----------- ----
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PACK_REVERSE_ROW_ORDER_ANGLE B GetIntegerv FALSE Pixel pack row order reversal 4.3.1
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New Implementation Dependent State
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None
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Issues
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None
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Sample Code
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/* Allocate space to hold the pixel data */
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const GLvoid* pixels = malloc(width * height * 4);
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/* Bind the framebuffer object to be read */
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glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
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/* Enable row order reversal */
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glPixelStore(GL_PACK_REVERSE_ROW_ORDER_ANGLE, TRUE);
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/* The pixel data stored in pixels will be in top-down order, ready for
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* use with a windowing system API that expects this order.
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*/
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glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
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Revision History
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Revision 1, 2011/11/22 (Brian Salomon)
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- First version
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Revision 2, 2012/02/22 (dgkoch)
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- prepare for publishing
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