c++ - 无法使用Opengl绘制三角形

Question

在这段代码中，我想使用 openGL 在蓝色背景上绘制一个简单的三角形，但是当我编译并运行代码时，只出现一个带有蓝色背景的窗口(没有应该绘制的白色三角形)，我正在使用代码

我的代码

#include <iostream>
#include <string>
#include <GLUT/glut.h>
#include <OpenGL/gl3.h>
#include <fstream>

using namespace std;

// VAO & VBO objects
GLuint VBO;
GLuint VAO;

void display();

// vertex Data (position)
float vertex[] = {-1.0, 0.0 , 1.0,
                   0.0, 1.0 , 0.0,
                   0.0, 0.0 , 0.0 };

GLuint Program;

GLuint Vshader;
GLuint Fshader;

// main program

int main (int argc, char *argv[])

{    

   glutInit(&argc, argv);
   glutInitDisplayMode(GLUT_DOUBLE);
   glutInitWindowSize(1000, 400);
   glutInitWindowPosition(100, 100);
   glutCreateWindow("My First GLUT/OpenGL Window");
   glutDisplayFunc(display);
   glutMainLoop();


   return 0;
}



// main display function 

void display()

{
// reading the vertex shader

fstream VertexS;
VertexS.open("/Users/hawbashali/Desktop/Project X/BwlbWl/BwlbWl/vertexShader");

if(VertexS.good() == false)
    cout << "Error openning the file \n";
if(VertexS.bad() == true)
    cout << "Read/writing error on i/o operation \n";
if (VertexS.fail() == true)
    cout <<"Logical error on i/o operation \n";

VertexS.seekg(0,ios::end);
int size =  (int)VertexS.tellg();
VertexS.clear();
VertexS.seekg(0,ios::beg);

char* vBuffer = new (nothrow) char[size];

VertexS.read(vBuffer,size);

VertexS.close();



// reading fragment shader

fstream FragS;
FragS.open("/Users/hawbashali/Desktop/Project X/BwlbWl/BwlbWl/fragmentShader");

if(FragS.good() == false)
    cout << "Error openning the file \n";
if(FragS.bad() == true)
    cout << "Read/writing error on i/o operation \n";
if (FragS.fail() == true)
    cout <<"Logical error on i/o operation \n";

FragS.seekg(0,ios::end);
int size2 =  (int)FragS.tellg();
FragS.clear();
FragS.seekg(0,ios::beg);

char* fBuffer = new (nothrow) char[size2];

FragS.read(fBuffer,size2);

FragS.close();


// creating shaders

Vshader = glCreateShader(GL_VERTEX_SHADER);
Fshader = glCreateShader(GL_FRAGMENT_SHADER);

GLint x = size;
GLint y = size2;


glShaderSource(Vshader, 1,(const char**)&vBuffer, &x);
glShaderSource(Fshader, 1, (const char**)&fBuffer, &y);

glCompileShader(Vshader);
glCompileShader(Fshader);

Program = glCreateProgram();

glAttachShader(Program, Vshader);
glAttachShader(Program, Fshader);

glLinkProgram(Program);

glUseProgram(Program);



glClearColor(0, 0, 1,1);
glClear(GL_COLOR_BUFFER_BIT);

glGenBuffers(1,&VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER,9 *sizeof(vertex),vertex, GL_STATIC_DRAW);

glEnableVertexAttribArray(0);

glVertexAttribPointer(0, 3,GL_FLOAT, GL_TRUE, 0, 0);

// Drawing the triangle
glDrawArrays(GL_TRIANGLES, 0, 3);

glDisableVertexAttribArray(0);

glutSwapBuffers();

glDeleteShader(Vshader);
glDeleteShader(Fshader);

delete [] vBuffer;
delete [] fBuffer;

};

顶点着色器:

#version 320 core
layout(location = 0) in vec4 vPosition;
void
main()
 {
     gl_Position = vPosition;
}

片段着色器

#version 320 core
out vec4 fColor;
void
main()
{
  fColor = vec4(0.0, 0.0, 1.0, 1.0);
}

Answer 1

glClearColor(0, 0, 1,1);
...
fColor = vec4(0.0, 0.0, 1.0, 1.0);

您正在尝试在蓝色背景上绘制一个蓝色三角形。你必须调高对比度 pretty high看到那个:)

将其中一个设为不同的颜色，例如红色。

你也是:

• 缺少 VAO
• 不请求核心上下文
• 使用#version 320 core instead of #version 150 core

试试这个:

#include <GL/glew.h>
#include <GL/freeglut.h>
#include <vector>
#include <iostream>

struct Program
{
    static GLuint Load( const char* vert, const char* geom, const char* frag )
    {
        GLuint prog = glCreateProgram();
        if( vert ) AttachShader( prog, GL_VERTEX_SHADER, vert );
        if( geom ) AttachShader( prog, GL_GEOMETRY_SHADER, geom );
        if( frag ) AttachShader( prog, GL_FRAGMENT_SHADER, frag );
        glLinkProgram( prog );
        CheckStatus( prog );
        return prog;
    }

private:
    static void CheckStatus( GLuint obj )
    {
        GLint status = GL_FALSE, len = 10;
        if( glIsShader(obj) )   glGetShaderiv( obj, GL_COMPILE_STATUS, &status );
        if( glIsProgram(obj) )  glGetProgramiv( obj, GL_LINK_STATUS, &status );
        if( status == GL_TRUE ) return;
        if( glIsShader(obj) )   glGetShaderiv( obj, GL_INFO_LOG_LENGTH, &len );
        if( glIsProgram(obj) )  glGetProgramiv( obj, GL_INFO_LOG_LENGTH, &len );
        std::vector< char > log( len, 'X' );
        if( glIsShader(obj) )   glGetShaderInfoLog( obj, len, NULL, &log[0] );
        if( glIsProgram(obj) )  glGetProgramInfoLog( obj, len, NULL, &log[0] );
        std::cerr << &log[0] << std::endl;
        exit( -1 );
    }

    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 );
    }
};

#define GLSL(version, shader) "#version " #version "\n" #shader

const char* vert = GLSL
( 
    150 core,
    layout(location = 0) in vec4 vPosition;
    void
    main()
    {
        gl_Position = vPosition;
    }
);

const char* frag = GLSL
( 
    150 core,
    out vec4 fColor;
    void
    main()
    {
        fColor = vec4(1.0, 0.0, 0.0, 1.0);
    }
);

// VAO & VBO objects
GLuint VAO;
GLuint VBO;
GLuint prog;
void init()
{
    // vertex Data (position)
    float vertex[] = { -1.0, -1.0 , 0.0,
                        1.0, -1.0 , 0.0,
                        0.0,  1.0 , 0.0 };

    glGenVertexArrays( 1, &VAO );
    glBindVertexArray( VAO );

    glGenBuffers(1,&VBO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, 9 * sizeof(vertex), vertex, GL_STATIC_DRAW);

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

    glEnableVertexAttribArray(0);
    glVertexAttribPointer( 0, 3, GL_FLOAT, GL_FALSE, 0, 0 );
}

void display()
{
    glClearColor(0, 0, 1,1);
    glClear(GL_COLOR_BUFFER_BIT);

    // Drawing the triangle
    glDrawArrays(GL_TRIANGLES, 0, 3);
    glutSwapBuffers();
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE );
    glutInitWindowSize(1000, 400);
    glutInitWindowPosition(100, 100);
    glutInitContextVersion(3, 2);
    glutInitContextProfile(GLUT_CORE_PROFILE);
    glutCreateWindow("My First GLUT/OpenGL Window");

    glewExperimental = GL_TRUE;
    if( GLEW_OK != glewInit() )
        return -1;

    init();

    glutDisplayFunc(display);
    glutMainLoop();
    return 0;
}

编辑:移植到 GL 2.1:

#include <GL/glew.h>
#include <GL/glut.h>
#include <vector>
#include <iostream>

struct Program
{
    static GLuint Load( const char* vert, const char* geom, const char* frag )
    {
        GLuint prog = glCreateProgram();
        if( vert ) AttachShader( prog, GL_VERTEX_SHADER, vert );
        if( geom ) AttachShader( prog, GL_GEOMETRY_SHADER, geom );
        if( frag ) AttachShader( prog, GL_FRAGMENT_SHADER, frag );
        glLinkProgram( prog );
        CheckStatus( prog );
        return prog;
    }

private:
    static void CheckStatus( GLuint obj )
    {
        GLint status = GL_FALSE, len = 10;
        if( glIsShader(obj) )   glGetShaderiv( obj, GL_COMPILE_STATUS, &status );
        if( glIsProgram(obj) )  glGetProgramiv( obj, GL_LINK_STATUS, &status );
        if( status == GL_TRUE ) return;
        if( glIsShader(obj) )   glGetShaderiv( obj, GL_INFO_LOG_LENGTH, &len );
        if( glIsProgram(obj) )  glGetProgramiv( obj, GL_INFO_LOG_LENGTH, &len );
        std::vector< char > log( len, 'X' );
        if( glIsShader(obj) )   glGetShaderInfoLog( obj, len, NULL, &log[0] );
        if( glIsProgram(obj) )  glGetProgramInfoLog( obj, len, NULL, &log[0] );
        std::cerr << &log[0] << std::endl;
        exit( -1 );
    }

    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 );
    }
};

#define GLSL(version, shader) "#version " #version "\n" #shader

const char* vert = GLSL
( 
    120,
    attribute vec4 vPosition;
    void main()
    {
        gl_Position = vPosition;
    }
);

const char* frag = GLSL
( 
    120,
    void main()
    {
        gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
    }
);

// VBO objects
GLuint VBO;
GLuint prog;
void init()
{
    // vertex Data (position)
    float vertex[] = { -1.0, -1.0 , 0.0,
                        1.0, -1.0 , 0.0,
                        0.0,  1.0 , 0.0 };

    glGenBuffers(1,&VBO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, 9 * sizeof(vertex), vertex, GL_STATIC_DRAW);

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

    int posLoc = glGetAttribLocation( prog, "vPosition" );
    glEnableVertexAttribArray( posLoc );
    glVertexAttribPointer( posLoc, 3, GL_FLOAT, GL_FALSE, 0, 0 );
}

void display()
{
    glClearColor(0, 0, 1,1);
    glClear(GL_COLOR_BUFFER_BIT);

    // Drawing the triangle
    glDrawArrays(GL_TRIANGLES, 0, 3);
    glutSwapBuffers();
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE );
    glutInitWindowSize(1000, 400);
    glutInitWindowPosition(100, 100);
    glutCreateWindow("My First GLUT/OpenGL Window");

    if( GLEW_OK != glewInit() )
        return -1;

    init();

    glutDisplayFunc(display);
    glutMainLoop();
    return 0;
}