openGL API-glGetUniformLocation

Name

glGetUniformLocation — Returns the location of a uniform variable

C Specification

`GLint glGetUniformLocation(`	GLuint program,
	const GLchar *name`)`;

Parameters

program

Specifies the program object to be queried.

name

Points to a null terminated string containing the name of the uniform variable whose location is to be queried.

Description

glGetUniformLocation returns an integer that represents the location of a specific uniform variable within a program object. name must be a null terminated string that contains no white space. name must be an active uniform variable name in program that is not a structure, an array of structures, or a subcomponent of a vector or a matrix. This function returns -1 if name does not correspond to an active uniform variable in program, if name starts with the reserved prefix "gl_", or if name

Uniform variables that are structures or arrays of structures may be queried by calling glGetUniformLocation for each field within the structure. The array element operator "[]" and the structure field operator "." may be used in name in order to select elements within an array or fields within a structure. The result of using these operators is not allowed to be another structure, an array of structures, or a subcomponent of a vector or a matrix. Except if the last part of name

The actual locations assigned to uniform variables are not known until the program object is linked successfully. After linking has occurred, the command glGetUniformLocation can be used to obtain the location of a uniform variable. This location value can then be passed to glUniform to set the value of the uniform variable or to glGetUniform in order to query the current value of the uniform variable. After a program object has been linked successfully, the index values for uniform variables remain fixed until the next link command occurs. Uniform variable locations and values can only be queried after a link if the link was successful.

Errors

GL_INVALID_VALUE is generated if program

GL_INVALID_OPERATION is generated if program

Associated Gets

glGetActiveUniform with arguments program

glGetProgram with arguments program and GL_ACTIVE_UNIFORMS or GL_ACTIVE_UNIFORM_MAX_LENGTH

glGetUniform with arguments program

glIsProgram

Version Support

												OpenGL Version
Function / Feature Name	2.0	2.1	3.0	3.1	3.2	3.3	4.0	4.1	4.2	4.3	4.4	4.5
`glGetUniformLocation`	✔	✔	✔	✔	✔	✔	✔	✔	✔	✔	✔	✔

Copyright

Copyright © 2003-2005 3Dlabs Inc. Ltd. Copyright © 2010-2014 Khronos Group. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.

# 翻译

名称

glGetUniformLocation- 返回统一变量的位置（获取一致变量在着色器程序中的位置序号，通过该序号可以设置一致变量的值，如果没有该变量则返回-1）

C规范

GLint glGetUniformLocation（GLuint program,const GLchar *name）;

参数

program

指定要查询的程序对象。

name

要查询其位置的统一变量的名称。

描述

glGetUniformLocation返回一个整数，表示程序对象中特定统一变量的位置。 name必须是不包含空格的空终止字符串。 name必须是程序中的活动统一变量名，它不能是结构，也不能是结构数组或向量或矩阵的子组件。如果name与程序中的活动统一变量不对应，或者name以保留前缀“gl_”开头，则此函数返回-1。

可以通过为结构中的每个字段调用glGetUniformLocation来查询作为结构或结构数组的统一变量。数组元素运算符“[]”和结构字段运算符“.” 可以在name中使用，以便选择数组中的元素或结构中的字段。使用这些运算符的结果不允许是另一个结构，结构数组或向量或矩阵的子组件。除非name的最后一部分表示统一变量数组，否则可以使用数组的名称或使用“[0]”附加的名称来检索数组的第一个元素的位置。

在程序对象成功链接之前，分配给统一变量的实际位置是不知道的。发生链接后，命令glGetUniformLocation可用于获取统一变量的位置。然后可以将此位置值传递给glUniform以设置统一变量的值或glGetUniform以查询统一变量的当前值。成功链接程序对象后，统一变量的索引值保持不变，直到发生下一个链接命令。如果链接成功，则只能在链接后查询统一变量位置和值。

错误

GL_INVALID_VALUE ：program不是OpenGL生成的值。

GL_INVALID_OPERATION ：program不是程序对象。

GL_INVALID_OPERATION ：program没有成功链接。

举个栗子：

在openGL中，我们创建100个平移向量，它包含着10×10格子所有位置。除了生成 translations 数组
外，我们还需要把这些位移数据发送到顶点着色器的uniform数组：

shader.Use();
for(GLuint i = 0; i < 100; i++)
{
stringstream ss;
string index;
ss << i;
index = ss.str();
GLint location = glGetUniformLocation(shader.Program, ("offsets[" + index + "]").c
_str())
glUniform2f(location, translations[i].x, translations[i].y);
}

这段代码的意思是：有100个正方体，他们有各自的顶点位置保存在数组 offset[100],向shader中传递offset[100]这个数组，顶点着色器shader中的代码可能是：

#version 330 core
layout (location = 0) in vec2 position;
layout (location = 1) in vec3 color;
out vec3 fColor;
uniform vec2 offsets[100];
void main()
{
vec2 offset = offsets[gl_InstanceID];
gl_Position = vec4(position + offset, 0.0f, 1.0f);
fColor = color;
}

另见

glLinkProgram，glUniform

版权

https://www.khronos.org/registry/OpenGL-Refpages/es2.0/xhtml/glGetUniformLocation.xml

参考

flycatdeng

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