| Name |
| |
| CHROMIUM_bind_uniform_location |
| |
| Name Strings |
| |
| GL_CHROMIUM_bind_uniform_location |
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| Version |
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| Last Modifed Date: September 8, 2015 |
| |
| Dependencies |
| |
| OpenGL ES 2.0 is required. |
| |
| Overview |
| |
| This extension is simlar to glBindAttribLocation but instead |
| lets you choose a location for a uniform. This allows you |
| to not have to query the locations of uniforms. |
| |
| This allows the client program to know the locations of uniforms |
| without having to wait for shaders to compile or GLSL programs to |
| link to query the locations and therefore have no blocking calls |
| when initializing programs. |
| |
| Issues |
| |
| If a uniform is an array you can only call glBindUniformLocation |
| for the location of the first element. Other elements' locations |
| must be queried if you need them. Often this is not an issue |
| because you can set all the elements with a single gl call from |
| the first location. |
| |
| Good Example: |
| |
| --shader-- |
| uniform float u_someArray[4]; |
| |
| --C-- |
| GLint location = 123; |
| glBindUniformLocation(program, location, "u_someArray"); |
| glLinkProgram(program); |
| glUseProgram(program); |
| |
| // set all 4 floats in u_someArray |
| float values[] = { 0.1f, 0.2f, 0.3f, 0.4f, }; |
| glUniform1fv(location, 4, values); |
| |
| Bad example 1: |
| |
| GLint location = 123; |
| glBindUniformLocation(program, location, "u_someArray"); |
| glLinkProgram(program); |
| glUseProgram(program); |
| |
| // set floats in u_someArray one at a time |
| glUniform1f(location, 0.1f); |
| glUniform1f(location + 1, 0.2f); // ERROR! math not allowed on locations |
| |
| Bad example 2: |
| |
| GLint location0 = 123; |
| GLint location1 = 124; |
| glBindUniformLocation(program, location0, "u_someArray[0]"); |
| glBindUniformLocation(program, location1, "u_someArray[1]"); // ERROR! |
| // not allowed to assign locations to array elements |
| |
| If you need to set individual elements of a uniform array you must query the |
| location of the each element you wish to set. |
| |
| If a uniform has its location explicitly set within the shader text and a |
| different location set via the API, the assignment in the shader text is |
| used. |
| |
| If the location of a statically used uniform set via the API conflicts with |
| the location of a different uniform set in the shader text, linking must |
| fail. |
| |
| New Tokens |
| |
| None |
| |
| New Procedures and Functions |
| |
| void BindUniformLocationCHROMIUM (GLuint program, GLint location, |
| const GLhchar* name); |
| |
| specifes that the uniform variable named <name> in program <program> |
| should be bound to uniform location <location> when the program is next |
| linked. If <name> was bound previously, its assigned binding is replaced |
| with <location>. <name> must be a null terminated string. The error |
| INVALID_VALUE is generated if <location> is equal or greater than |
| |
| (MAX_VERTEX_UNIFORM_VECTORS + MAX_FRAGMENT_UNIFORM_VECTORS) * 4 |
| |
| or less than 0. BindUniformLocation has no effect until the program is |
| linked. In particular, it doesn't modify the bindings of active uniforms |
| variables in a program that has already been linked. |
| |
| The error INVALID_OPERATION is generated if name starts with the reserved |
| "gl_" prefix. The error INVALID_VALUE is generated if name ends with |
| an array element expression other than "[0]". |
| |
| When a program is linked, any active uniforms without a binding specified |
| through BindUniformLocation will be automatically be bound to locations by |
| the GL. Such bindings can be queried using the command |
| GetUniformLocation. |
| |
| BindUniformLocation may be issued before any shader objects are attached |
| to a program object. Hence it is allowed to bind any name (except a name |
| starting with "gl_") to an index, including a name that is never used as a |
| uniform in any shader object. Assigned bindings for uniform variables |
| that do not exist or are not active are ignored. Using such bindings |
| behaves as if passed location was -1. |
| |
| It is possible for an application to bind more than one uniform name to |
| the same location. This is referred to as aliasing. This will only work |
| if only one of the aliased uniforms is active in the executable program, |
| or if no path through the shader consumes more than one uniform of a set |
| of uniforms aliased to the same location. If two statically used uniforms |
| in a program are bound to the name location, link must fail. |
| |
| Errors |
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| None. |
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| New State |
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| None. |
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| Revision History |
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| 7/20/2012 Documented the extension |
| 9/8/2015 Require program link to fail if two statically used uniforms |
| are bound to the same location. |
| 11/6/2015 Require inactive and non-existing, bound uniform locations |
| to behave like location -1. |
| 3/9/2017 Locations set in the shader override ones set by the binding |
| API. |