问题

大家好，我正在学习 WebGL，但无法获取特殊变量的位置。
以下是代码

顶点着色器

uniform vec2 u_translation;
attribute vec2 a_position;
uniform vec2 u_resolution;
void main() {
vec2 position = a_position + u_translation;
vec2 zeroToOne = a_position / u_resolution;
vec2 zeroToTwo = zeroToOne * 2.0;
vec2 clipSpace = zeroToTwo - 1.0;
gl_Position = vec4(clipSpace * vec2(1, -1), 0, 1);
}

片元着色器

precision mediump float;
uniform vec4 u_color;
void main() {
gl_FragColor = u_color;
}

var translationLocation = gl.getUniformLocation(program, "u_translation");
var positionLocation = gl.getAttribLocation(program, "a_position");
var resolutionLocation = gl.getUniformLocation(program, "u_resolution");
var colorLocation = gl.getUniformLocation(program, "u_color");
// translationLocation 为 null，但其他变量可以获取到

[查看图片描述](https://i.stack.imgur.com/6J6sc.png)



有人知道发生了什么吗？我认为我在着色器中使用了 'u_translation'

  uniform vec2 u_translation;
  attribute vec2 a_position;
  uniform vec2 u_resolution;
  void main() {
    vec2 position = a_position + u_translation;
    vec2 zeroToOne = a_position / u_resolution;
    vec2 zeroToTwo = zeroToOne * 2.0;
    vec2 clipSpace = zeroToTwo - 1.0;
    gl_Position = vec4(clipSpace * vec2(1, -1), 0, 1);
  }

  precision mediump float;
  uniform vec4 u_color;
  void main() {
    gl_FragColor = u_color;
  }

    var translationLocation = gl.getUniformLocation(program, "u_translation");
    var positionLocation = gl.getAttribLocation(program, "a_position");
    var resolutionLocation = gl.getUniformLocation(program, "u_resolution");
    var colorLocation = gl.getUniformLocation(program, "u_color");
// translationLocation is null  but i can get the others

答案1

得分: 0

本地变量 `position` 在着色器中未被使用，因此不需要 `u_translation` 并且被优化掉。因此它不会成为一个活动的程序资源，也不会得到统一位置。可能以下行错误：

>```glsl
>vec2 zeroToOne = a_position / u_resolution;
>```

但应该是：

```glsl
vec2 zeroToOne = position / u_resolution;

现在本地变量 position 在着色器程序中被使用，因此 u_translation 成为一个活动的程序资源。

<details>
<summary>英文:</summary>

The local variable `position` is not used anywhere in the shader and thus `u_translation` is not needed and optimized out. So it does not become an active program resource and does not get a uniform location. Likely the following line is wrong

&gt;```glsl
&gt;vec2 zeroToOne = a_position / u_resolution;
&gt;```

but should be

```glsl
vec2 zeroToOne = position / u_resolution;

Now the local variable position is used in the shader program and thus u_translation becomes an active program resource.