opengl - GLSL 1.5 和 OpenGL 3.3 : Passing color to vertex shader seems to fail

Question

将顶点属性传递给正在运行的着色器程序时出现问题。我想传递两个属性，位置和 RGBA 颜色。绑定(bind)属性位置适用于位置。但是，它不适用于颜色。因此，所有几何体最终都呈现为黑色。

这就是我所做的:

GLuint programHandler;

// create program
// compile & attach vertex shader
// compile & attach fragment shader

glBindAttribLocation(programHandler, 0, "InPosition");
glBindAttribLocation(programHandler, 1, "InColor");
glBindFragDataLocation(programHandler, 1, "FragColor");

glLinkProgram(programHandler);
glUseProgram(programHandler);

// initialize uniform variables

// I'm trying to get the attribute locations now.
// I expect location "0" for InPosition and location "1" for InColor.
// In fact, it gets me a "-1" for InColor. I simply cannot see the reason for that behaviour

GLint positionLocation = glGetAttribLocation(programHandler, "InPosition"); // returns 0
GLint colorLocation = glGetAttribLocation(programHandler, "InColor"); // returns -1

glEnableVertexAttribArray(positionLocation);
glEnableVertexAttribArray(colorLocation); // fails!

我的顶点着色器非常基础。我真正要做的就是转换顶点并将颜色传递给片段着色器:

#version 150 core

// input
uniform mat4 ModelviewMatrix;
uniform mat4 ProjectionMatrix;
in vec3 InPosition;
in vec4 InColor;

// output
out vec4 PassColor;

void main(void) {
    // passing color through to fragment shader
    PassColor = InColor;

    // transformation
    gl_Position = ProjectionMatrix * ModelviewMatrix * vec4(InPosition, 1.0);
}

我的片段着色器应该简单地返回该颜色:

#version 150 core
precision highp float;

// input
in vec4 PassColor;

// output
out vec4 FragColor;

void main(void) {
    FragColor = PassColor;
}

为什么绑定(bind)“InPosition”有效而“InColor”无效？我知道 GLSL 编译器优化了着色器代码，因此无法绑定(bind)未使用的变量。但是，我不明白为什么应该在这里优化颜色。毕竟，我通过将它传递给片段着色器来使用它。

Answer 1

盲目射击，我认为这是错误的:

glBindFragDataLocation(programHandler, 1, "FragColor");

它应该是:

glBindFragDataLocation(programHandler, 0, "FragColor");