C++ 与GLSL相关的OpenGL应用程序代码

我很难理解OpenGL应用程序和GLSL文件（.vert和.frag）之间的连接。我知道如何创建顶点或片段着色器，网络上有很多示例，但我在应用程序中实际使用着色器时遇到困难，特别是将纹理链接（绑定？）到着色器。我的问题是，我缺少什么代码来使用我上传到应用程序中的纹理和着色器

我当前的应用程序创建一个窗口，加载4个纹理（岩石、草地、石头和一个混合贴图，因为我想将其用于纹理飞溅），然后在主循环中绘制一个四边形。我的整个应用程序代码如下：

#include <windows.h>
#include <iostream>
#include <sstream>
#include <fstream>
#include <SFML/Graphics.hpp>
#include <glew.h>
#include <gl/gl.h>
#include <gl/glu.h>

#include "textfile.h"
#include "textfile.cpp"

using namespace std;

class Scene {
public:
    void resize( int w, int h ) {
        // OpenGL Reshape
        glViewport( 0, 0, w, h );
        glMatrixMode( GL_PROJECTION );
        glLoadIdentity();
        gluPerspective( 120.0, (GLdouble)w/(GLdouble)h, 0.5, 500.0 );
        glMatrixMode( GL_MODELVIEW );
    }
};

///Shader
GLuint p, f, v;
void setShader() {

    char *vs,*fs;

    v = glCreateShader(GL_VERTEX_SHADER);
    f = glCreateShader(GL_FRAGMENT_SHADER);

    vs = textFileRead("shader.vert");
    fs = textFileRead("shader.frag");

    const char * vv = vs;
    const char * ff = fs;

    glShaderSource(v, 1, &vv,NULL);
    glShaderSource(f, 1, &ff,NULL);

    free(vs);free(fs);

    glCompileShader(v);
    glCompileShader(f);

    p = glCreateProgram();

    glAttachShader(p,v);
    glAttachShader(p,f);

    glLinkProgram(p);
    glUseProgram(p);
}

int main() {

    sf::RenderWindow window(sf::VideoMode(800, 600, 32), "Test");

    ///Setup the scene, materials, lighting
    Scene scene;
    scene.resize(800,600);
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_LIGHTING);
    glColorMaterial(GL_FRONT_AND_BACK, GL_EMISSION);
    glEnable(GL_COLOR_MATERIAL);
    glShadeModel(GL_SMOOTH);

    ///Terrain Textures
    sf::Image tex0;
    tex0.loadFromFile("mixmap.png");
    sf::Image tex1;
    tex1.loadFromFile("grass.png");
    sf::Image tex2;
    tex2.loadFromFile("rock.png");
    sf::Image tex3;
    tex3.loadFromFile("stone.png");

    GLuint mixmap;
    glGenTextures(1, &mixmap);
    glBindTexture(GL_TEXTURE_2D, mixmap);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, tex0.getSize().x, tex0.getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, (const GLvoid*)tex0.getPixelsPtr() );

    GLuint grass;
    glGenTextures(1, &grass);
    glBindTexture(GL_TEXTURE_2D, grass);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, tex1.getSize().x, tex1.getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, (const GLvoid*)tex1.getPixelsPtr() );

    GLuint rock;
    glGenTextures(1, &rock);
    glBindTexture(GL_TEXTURE_2D, rock);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, tex2.getSize().x, tex2.getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, (const GLvoid*)tex2.getPixelsPtr() );

    GLuint stone;
    glGenTextures(1, &stone);
    glBindTexture(GL_TEXTURE_2D, stone);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, tex3.getSize().x, tex3.getSize().y, 0, GL_RGBA, GL_UNSIGNED_BYTE, (const GLvoid*)tex3.getPixelsPtr() );

    ///I am afrain I am missing some code here that will actually link the textures to the shader itself

    ///Shader
    glewInit();
    setShader();

    ///Start loop
    while( window.isOpen() ) {
        sf::Event event;
        while( window.pollEvent( event ) ) {
            if( event.type == sf::Event::Closed )
                window.close();
        }

        glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        gluPerspective(50.0, 1.0, 1.0, 50);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        gluLookAt(1, 0, 1, 0, 0, 0, 0, 1, 0);

        glBegin(GL_QUADS);
            glVertex3f(-0.5, -0.5, 0.0);

            glVertex3f(-0.5, 0.5, 0.0);

            glVertex3f(0.5, 0.5, 0.0);

            glVertex3f(0.5, -0.5, 0.0);
        glEnd();

        ///Reset env settings for SFML
        glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

        window.display();
    }
    return 1;
}

片段：

uniform sampler2D MixMap;
uniform sampler2D Grass;
uniform sampler2D Stone;
uniform sampler2D Rock;

varying vec4 texCoord;

void main(void)
{
   vec4 mixmap   = texture2D( MixMap, texCoord.xy );
   vec4 tex0    = texture2D( Grass, texCoord.xy ); 
   vec4 tex1    = texture2D( Rock,  texCoord.xy ); 
   vec4 tex2    = texture2D( Stone, texCoord.xy );

   tex0 *= mixmap.r; 
   tex1 = mix( tex0, tex1, mixmap.g ); 
   vec4 outColor = mix( tex1, tex2, mixmap.b ); 

   gl_FragColor = outColor;
}

您需要同时使用和来告诉着色器程序哪些纹理附加到哪些采样器

示例如下：

---

首先，需要将每个纹理对象绑定到OpenGL上下文中的纹理单元。GPU具有

GL\u MAX\u组合的纹理图像单元

纹理图像单元的数量，每个纹理图像单元都可以附加纹理

这看起来像这样：

glActiveTexture(GL_TEXTURE0 + 0);
glBindTexture(GL_TEXTURE_2D, mixmap); //mixmap now attached to sampler 0

glActiveTexture(GL_TEXTURE0 + 1);
glBindTexture(GL_TEXTURE_2D, grass); //attached to sampler 1

glActiveTexture(GL_TEXTURE0 + 2);
glBindTexture(GL_TEXTURE_2D, rock);  //attached to sampler 2

glActiveTexture(GL_TEXTURE0 + 3);
glBindTexture(GL_TEXTURE_2D, stone); //attached to sampler 3

注意

GL\u TEXTURE0

+x语法。这样做的目的是，您不会感到受到

GL_TEXTUREi

的约束，只会进入

GL_TEXTURE32

；您可以有32个以上的同时多重纹理（如果您的实现支持）。当然，我不知道你为什么想，但你可以

现在有四个纹理绑定到四个纹理图像单元。下一步是将GLSL采样器指定给纹理图像单元。链接着色器后，必须查询每个采样器的统一位置，然后告诉程序应查找实际纹理的纹理图像单元

compileAndLinkProgram();
glUseProgram(program);

mixmapUniformLocation = glGetUniformLocation(program, "MixMap"); //get the uniform associated with "MixMap"
glUniform1i(mixmapUniformLocation, 0); //set MixMap uniform to 0 (sampler 0);


grassUniformLocation = glGetUniformLocation(program, "Grass"); //get the uniform associated with "Grass"
glUniform1i(grassUniformLocation, 1); //set Grass uniform to 1 (sampler 1);

...repeat for 4 samplers...

---

现在，当您在着色器中采样采样器时，它将从绑定到该采样器的纹理中提取

不完全准确。glUniform不会告诉着色器程序哪些纹理附加到哪些采样器。它告诉着色器将哪个采样器变量（例如Grass、Stone）指定给哪个采样器索引<代码>glActiveTexture/glBindTexture将纹理指定给采样器单元。不将纹理附加到采样器。将纹理绑定到上下文中的纹理图像单元，然后告诉程序它的采样器在上下文中使用特定的纹理图像单元。这是一种间接关联。@Nicol Bolas您愿意编辑正确的术语吗？恐怕我不太明白采样器和纹理图像单元之间的区别。即使是看起来模棱两可的“但请确保使用glActiveTexture（GL_TEXTURE14）将纹理绑定到正确的采样器”感谢您提醒我该wiki页面，以便我可以使用nuke。将来，您可能希望参考以获得更准确的信息。

compileAndLinkProgram();
glUseProgram(program);

mixmapUniformLocation = glGetUniformLocation(program, "MixMap"); //get the uniform associated with "MixMap"
glUniform1i(mixmapUniformLocation, 0); //set MixMap uniform to 0 (sampler 0);


grassUniformLocation = glGetUniformLocation(program, "Grass"); //get the uniform associated with "Grass"
glUniform1i(grassUniformLocation, 1); //set Grass uniform to 1 (sampler 1);

...repeat for 4 samplers...