顶点属性的插值

Question

我正在尝试将距离作为顶点属性从我的 C++ 代码传递到在两个顶点之间绘制一条线的着色器中。

当前一行的距离为 0（开始），另一行的距离为 1.0。我希望这个值像颜色一样被插值，但它似乎不起作用。因此，我希望线的一半是红色，另一半是绿色，但整条线都是绿色的。

下面的片段着色器代码，其中顶点着色器中的 dist 来自 float in_dist 中的布局（位置 = 2），并作为 out float dist（未执行任何操作）传递出去。

in float dist;

Fragment getFragment() 
{
    Fragment frag;
    frag.depth = vs_positionScreenSpace.w;

    frag.gPosition = vs_gPosition;

    if(dist > 0.5){
        frag.color = vec4(1.0,0.0,0.0,1.0);
    }else{
        frag.color = vec4(0.0,1.0,0.0,1.0);
    }

    frag.gNormal = vec4(0.0, 0.0, 1.0, 0.0);

    return frag;
}

顶点着色器

layout(location = 0) in vec3 in_point_position;
layout(location = 1) in vec4 in_color;
layout(location = 2) in float in_dist;

out float dist;

void main() {

    //somestuff....

    dist = in_dist;
}

Answer 1

在这里工作很好：

MCVE:

#include <GL/glew.h>
#include <GLFW/glfw3.h>
#include <vector>
#include <iostream>
#include <cstdarg>

struct Program
{
    static GLuint Load( const char* shader, ... )
    {
        GLuint prog = glCreateProgram();
        va_list args;
        va_start( args, shader );
        while( shader )
        {
            const GLenum type = va_arg( args, GLenum );
            AttachShader( prog, type, shader );
            shader = va_arg( args, const char* );
        }
        va_end( args );
        glLinkProgram( prog );
        CheckStatus( prog );
        return prog;
    }

private:
    static void CheckStatus( GLuint obj )
    {
        GLint status = GL_FALSE;
        if( glIsShader(obj) ) glGetShaderiv( obj, GL_COMPILE_STATUS, &status );
        if( glIsProgram(obj) ) glGetProgramiv( obj, GL_LINK_STATUS, &status );
        if( status == GL_TRUE ) return;
        GLchar log[ 1 << 15 ] = { 0 };
        if( glIsShader(obj) ) glGetShaderInfoLog( obj, sizeof(log), NULL, log );
        if( glIsProgram(obj) ) glGetProgramInfoLog( obj, sizeof(log), NULL, log );
        std::cerr << log << std::endl;
        std::exit( EXIT_FAILURE );
    }

    static void AttachShader( GLuint program, GLenum type, const char* src )
    {
        GLuint shader = glCreateShader( type );
        glShaderSource( shader, 1, &src, NULL );
        glCompileShader( shader );
        CheckStatus( shader );
        glAttachShader( program, shader );
        glDeleteShader( shader );
    }
};

const char* vert = R"GLSL(
#version 330 core
layout( location = 0 ) in vec4 inPos;
layout( location = 1 ) in float inDist;
out float dist;
void main()
{
    dist = inDist;
    gl_Position = inPos;
}
)GLSL";

const char* frag = R"GLSL(
#version 330 core
in float dist;
out vec4 outColor;
void main()
{
    if( dist > 0.5 )
    {
        outColor = vec4( 1.0, 0.0, 0.0, 1.0 );
    }
    else
    {
        outColor = vec4( 0.0, 1.0, 0.0, 1.0 );
    }
}
)GLSL";

int main( int argc, char** argv )
{
    glfwInit();
    glfwWindowHint( GLFW_CONTEXT_VERSION_MAJOR, 3 );
    glfwWindowHint( GLFW_CONTEXT_VERSION_MINOR, 3 );
    glfwWindowHint( GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE );
    GLFWwindow* window = glfwCreateWindow( 640, 480, "GLFW", NULL, NULL );
    glfwMakeContextCurrent( window );
    glewInit();
    glfwSwapInterval( 1 );

    GLuint prog = Program::Load( vert, GL_VERTEX_SHADER, frag, GL_FRAGMENT_SHADER, NULL );
    glUseProgram( prog );

    GLuint vao = 0;
    glGenVertexArrays( 1, &vao );
    glBindVertexArray( vao );

    GLuint vbo0 = 0;
    glGenBuffers( 1, &vbo0 );
    glBindBuffer( GL_ARRAY_BUFFER, vbo0 );
    std::vector<float> data0 =
    {
        -0.5f, -0.5f,
         0.5f,  0.5f,
    };
    glBufferData( GL_ARRAY_BUFFER, data0.size() * sizeof( std::vector<float>::value_type ), data0.data(), GL_STATIC_DRAW );
    glVertexAttribPointer( 0 , 2, GL_FLOAT, GL_FALSE, 0, 0 );
    glEnableVertexAttribArray( 0 );

    GLuint vbo1 = 0;
    glGenBuffers( 1, &vbo1 );
    glBindBuffer( GL_ARRAY_BUFFER, vbo1 );
    std::vector<float> data1 =
    {
        0.0f, 1.0f,
    };
    glBufferData( GL_ARRAY_BUFFER, data1.size() * sizeof( std::vector<float>::value_type ), data1.data(), GL_STATIC_DRAW );
    glVertexAttribPointer( 1 , 1, GL_FLOAT, GL_FALSE, 0, 0 );
    glEnableVertexAttribArray( 1 );

    while( !glfwWindowShouldClose( window ) )
    {
        glfwPollEvents();

        int w, h;
        glfwGetFramebufferSize( window, &w, &h );
        glViewport( 0, 0, w, h );

        glClear( GL_COLOR_BUFFER_BIT );

        glUseProgram( prog );
        glBindVertexArray( vao );
        glDrawArrays( GL_LINES, 0, 2 );

        glfwSwapBuffers( window );
    }

    glfwDestroyWindow( window );
    glfwTerminate();
}

Answer 2

已解决；结果证明问题不在着色器代码中，而是在如何定义顶点属性 att glVertexAttributePointer。

顶点属性的插值

Interpolation of a vertex attribute

opengl

shader

glsl

fragment-shader