不能用Opengl绘制三角形?

in this code i want to draw a simple triangle on a blue background using openGL however when i compile and run the code only a window with the blue background appears (without the white triangle that is supposed to be drawn), iam using Xcode

在这段代码中，我想使用openGL在蓝色背景上画一个简单的三角形，但是当我编译并运行代码时，只会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)，iam使用Xcode。

my code

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;

};

Vertex shader:

顶点着色器:

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

Fragment Shader

片段着色器

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

2 个解决方案

#1

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

You're trying to draw a blue triangle on top of a blue background. You'll have to dial up your contrast pretty high to see that :)

你想在蓝色背景上画一个蓝色三角形。你得把对比度调高才能看到:)

Make one of them a different color, like red.

让其中一个颜色不同，比如红色。

You're also:

你也:

• Missing a VAO
• 错过了农村村民
• Not requesting a Core context
• 不请求核心上下文。
• Using #version 320 core instead of #version 150 core
• 使用#版本320内核而不是#版本150内核。

Try this:

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;
}

EDIT: Ported to GL 2.1:

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;
}

#2

You have provided invalid buffer size in the following line:

您在以下行中提供了无效的缓冲区大小:

glBufferData(GL_ARRAY_BUFFER, 9 * sizeof(vertex), vertex, GL_STATIC_DRAW);

Because sizeof(vertex) should return the total size of the array (e.g 36) not the underlying type, thus no need to multiply by 9. If you still want to use multiplication try following:

因为sizeof(顶点)应该返回数组的总大小(e)。而不是底层类型，因此不需要乘以9。如果你仍然想使用乘法，请尝试:

9 * sizeof(float)

I have to write this down... You should separate your initialization and draw cycle like in genpfault's answer.

我得把这个写下来…您应该将初始化和绘制周期分开，就像genpfault的答案一样。