OpenGL学习（3）——Shader（补）

完成章节后练习。

练习

1. Adjust the vertex shader so that the triangle is upside down.

#version 330 core
layout (location = 0) in vec3 Pos;
layout (location = 1) in vec3 Col;
out vec4 Color;
void main()
{
    gl_Position = vec4(Pos.x, -Pos.y, Pos.z, 1.0f);
    Color = vec4(Col, 1.0f);
}

2. Specify a horizontal offset via a uniform and move the triangle to the right side of the screen in the vertex shader using this offset value.

#version 330 core
layout (location = 0) in vec3 Pos;
layout (location = 1) in vec3 Col;
uniform float offset;
out vec4 Color;
void main()
{
    gl_Position = vec4(Pos.x + offset, Pos.y, Pos.z, 1.0f);
    Color = vec4(Col, 1.0f);
}

ourShader.use();
float offset = 0.5;
int uniformlocation = glGetUniformLocation(ourShader.ID, "offset");
glUniform1f(uniformlocation, offset);

3. Output the vertex position to the fragment shader using the out keyword and set the fragment's color equal to this vertex position (see how even the vertex position values are interpolated across the triangle). Once you managed to do this; try to answer the following question: why is the bottom-left side of our triangle black?

#version 330 core
layout (location = 0) in vec3 Pos;
layout (location = 1) in vec3 Col;
out vec3 fragPos;
void main()
{
    gl_Position = vec4(Pos.x, Pos.y, Pos.z, 1.0f);
    fragPos = Pos;
}

#version 330 core
out vec4 FragColor;
in vec3 fragPos;
void main()
{
    FragColor = vec4(fragPos, 1.0f);
}

左上角顶点坐标（-0.5, 0.5, 0），右下角顶点坐标（0.5, -0.5, 0），在顶点间二分之一处插值得到的结果是（0, 0, 0），因此渲染成黑色。