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comparison: gfx/angle/extensions/ANGLE_texture_usage.txt

gfx/angle/extensions/ANGLE_texture_usage.txt

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1 Name
2
3 ANGLE_texture_usage
4
5 Name Strings
6
7 GL_ANGLE_texture_usage
8
9 Contributors
10
11 Nicolas Capens, TransGaming
12 Daniel Koch, TransGaming
13
14 Contact
15
16 Daniel Koch, TransGaming (daniel 'at' transgaming.com)
17
18 Status
19
20 Complete
21
22 Version
23
24 Last Modified Date: November 10, 2011
25 Version: 2
26
27 Number
28
29 OpenGL ES Extension #112
30
31 Dependencies
32
33 This extension is written against the OpenGL ES 2.0 Specification.
34
35 Overview
36
37 In some implementations it is advantageous to know the expected
38 usage of a texture before the backing storage for it is allocated.
39 This can help to inform the implementation's choice of format
40 and type of memory used for the allocation. If the usage is not
41 known in advance, the implementation essentially has to make a
42 guess as to how it will be used. If it is later proven wrong,
43 it may need to perform costly re-allocations and/or reformatting
44 of the texture data, resulting in reduced performance.
45
46 This extension adds a texture usage flag that is specified via
47 the TEXTURE_USAGE_ANGLE TexParameter. This can be used to
48 indicate that the application knows that this texture will be
49 used for rendering.
50
51 IP Status
52
53 No known IP claims.
54
55 New Procedures and Functions
56
57 None
58
59 New Tokens
60
61 Accepted as a value for <pname> for the TexParameter{if} and
62 TexParameter{if}v commands and for the <value> parameter of
63 GetTexParameter{if}v:
64
65 TEXTURE_USAGE_ANGLE 0x93A2
66
67 Accepted as a value to <param> for the TexParameter{if} and
68 to <params> for the TexParameter{if}v commands with a <pname> of
69 TEXTURE_USAGE_ANGLE; returned as possible values for <data> when
70 GetTexParameter{if}v is queried with a <value> of TEXTURE_USAGE_ANGLE:
71
72 NONE 0x0000
73 FRAMEBUFFER_ATTACHMENT_ANGLE 0x93A3
74
75 Additions to Chapter 2 of the OpenGL ES 2.0 Specification (OpenGL ES Operation)
76
77 None
78
79 Additions to Chapter 3 of the OpenGL ES 2.0 Specification (Rasterization)
80
81 Add a new row to Table 3.10 (Texture parameters and their values):
82
83 Name | Type | Legal Values
84 ------------------------------------------------------------
85 TEXTURE_USAGE_ANGLE | enum | NONE, FRAMEBUFFER_ATTACHMENT_ANGLE
86
87 Add a new section 3.7.x (Texture Usage) before section 3.7.12 and
88 renumber the subsequent sections:
89
90 "3.7.x Texture Usage
91
92 Texture usage can be specified via the TEXTURE_USAGE_ANGLE value
93 for the <pname> argument to TexParameter{if}[v]. In order to take effect,
94 the texture usage must be specified before the texture contents are
95 defined either via TexImage2D or TexStorage2DEXT.
96
97 The usage values can impact the layout and type of memory used for the
98 texture data. Specifying incorrect usage values may result in reduced
99 functionality and/or significantly degraded performance.
100
101 Possible values for <params> when <pname> is TEXTURE_USAGE_ANGLE are:
102
103 NONE - the default. No particular usage has been specified and it is
104 up to the implementation to determine the usage of the texture.
105 Leaving the usage unspecified means that the implementation may
106 have to reallocate the texture data as the texture is used in
107 various ways.
108
109 FRAMEBUFFER_ATTACHMENT_ANGLE - this texture will be attached to a
110 framebuffer object and used as a desination for rendering or blits."
111
112 Modify section 3.7.12 (Texture State) and place the last 3 sentences
113 with the following:
114
115 "Next, there are the three sets of texture properties; each consists of
116 the selected minification and magnification filters, the wrap modes for
117 <s> and <t>, and the usage flags. In the initial state, the value assigned
118 to TEXTURE_MIN_FILTER is NEAREST_MIPMAP_LINEAR, and the value for
119 TEXTURE_MAG_FILTER is LINEAR. <s> and <t> wrap modes are both set to
120 REPEAT. The initial value for TEXTURE_USAGE_ANGLE is NONE."
121
122
123 Additions to Chapter 4 of the OpenGL ES 2.0 Specification (Per-Fragment
124 Operations and the Framebuffer)
125
126 None
127
128 Additions to Chapter 5 of the OpenGL ES 2.0 Specification (Special
129 Functions):
130
131 None
132
133 Additions to Chapter 6 of the OpenGL ES 2.0 Specification (State and
134 State Requests)
135
136 None
137
138 Dependencies on EXT_texture_storage
139
140 If EXT_texture_storage is not supported, omit any references to
141 TexStorage2DEXT.
142
143 Errors
144
145 If TexParameter{if} or TexParamter{if}v is called with a <pname>
146 of TEXTURE_USAGE_ANGLE and the value of <param> or <params> is not
147 NONE or FRAMEBUFFER_ATTACHMENT_ANGLE the error INVALID_VALUE is
148 generated.
149
150 Usage Example
151
152 /* create and bind texture */
153 glGenTextures(1, &texture);
154 glActiveTexture(GL_TEXTURE0);
155 glBindTexture(GL_TEXTURE_2D, texture);
156
157 /* specify texture parameters */
158 glTexParameteri(GL_TEXTURE_2D, GL_*, ...); /* as before */
159
160 /* specify that we'll be rendering to the texture */
161 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_USAGE_ANGLE, GL_FRAMEBUFFER_ATTACHMENT_ANGLE);
162
163 glTexStorage2DEXT(GL_TEXTURE_2D, levels, ...); // Allocation
164 for(int level = 0; level < levels; ++level)
165 glTexSubImage2D(GL_TEXTURE_2D, level, ...); // Initialisation
166
167 Issues
168
169 1. Should there be a dynamic usage value?
170
171 DISCUSSION: We could accept a dynamic flag to indicate that a texture will
172 be updated frequently. We could map this to D3D9 dynamic textures. This would
173 allow us to avoid creating temporary surfaces when updating the texture.
174 However renderable textures cannot be dynamic in D3D9, which eliminates the
175 primary use case for this. Furthermore, the memory usage of dynamic textures
176 typically increases threefold when you lock it.
177
178 2. Should the texture usage be an enum or a bitfield?
179
180 UNRESOLVED. Using a bitfield would allow combination of values to be specified.
181 On the other hand, if combinations are really required, additional <pnames>
182 could be added as necessary. Querying a bitfield via the GetTexParameter command
183 feels a bit odd.
184
185 3. What should happen if TEXTURE_USAGE_ANGLE is set/changed after the texture
186 contents have been specified?
187
188 RESOLVED: It will have no effect. However, if the texture is redefined (for
189 example by TexImage2D) the new allocation will use the updated usage.
190 GetTexParameter is used to query the value of the TEXTURE_USAGE_ANGLE
191 state that was last set by TexParameter for the currently bound texture, or
192 the default value if it has never been set. There is no way to determine the
193 usage that was in effect at the time the texture was defined.
194
195 Revision History
196
197 Rev. Date Author Changes
198 ---- ----------- --------- ----------------------------------------
199 1 10 Nov 2011 dgkoch Initial revision
200 2 10 Nov 2011 dgkoch Add overview
201
202

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