c++ - 红皮书示例 1.1 不起作用

Question

我是 OpenGL 的新手，一直在努力遵循红皮书(第 8 版)。然而，在尝试运行第一个教程时，我遇到了一个问题。起初，我的 IDE (VS 2012) 发现了以下行的问题:

GLuint program = LoadShaders(shaders)

发现的问题是无法将 ShaderInfo[3] 转换为 ShaderInfo。我试图通过将行更改为来解决此问题:

GLuint program = LoadShaders(*shaders)

，这似乎奏效了一点。然而，在编译代码时，出现了一个错误( Unresolved external 问题)。我怀疑我早先尝试解决上述问题可能是原因，但在多次尝试代码无济于事之后，我决定问问知道他们在做什么的人。

错误信息

1>------ Build started: Project: sarpg, Configuration: Debug Win32 ------
1>  main.cpp
1>c:\users\callum\documents\visual studio 2012\projects\sarpg\sarpg\main.cpp(7): warning C4005: 'BUFFER_OFFSET' : macro redefinition
1>          c:\users\callum\documents\visual studio 2012\projects\sarpg\sarpg\vgl.h(55) : see previous definition of 'BUFFER_OFFSET'
1>c:\users\callum\documents\visual studio 2012\projects\sarpg\sarpg\main.cpp(23): warning C4305: 'initializing' : truncation from 'double' to 'GLfloat'
1>c:\users\callum\documents\visual studio 2012\projects\sarpg\sarpg\main.cpp(24): warning C4305: 'initializing' : truncation from 'double' to 'GLfloat'
1>c:\users\callum\documents\visual studio 2012\projects\sarpg\sarpg\main.cpp(25): warning C4305: 'initializing' : truncation from 'double' to 'GLfloat'
1>c:\users\callum\documents\visual studio 2012\projects\sarpg\sarpg\main.cpp(26): warning C4305: 'initializing' : truncation from 'double' to 'GLfloat'
1>c:\users\callum\documents\visual studio 2012\projects\sarpg\sarpg\main.cpp(27): warning C4305: 'initializing' : truncation from 'double' to 'GLfloat'
1>c:\users\callum\documents\visual studio 2012\projects\sarpg\sarpg\main.cpp(28): warning C4305: 'initializing' : truncation from 'double' to 'GLfloat'
1>main.obj : warning LNK4217: locally defined symbol _glewInit@0 imported in function _main
1>main.obj : warning LNK4049: locally defined symbol ___glewBindBuffer imported
1>main.obj : warning LNK4049: locally defined symbol ___glewBufferData imported
1>main.obj : warning LNK4049: locally defined symbol ___glewGenBuffers imported
1>main.obj : warning LNK4049: locally defined symbol ___glewUseProgram imported
1>main.obj : warning LNK4049: locally defined symbol ___glewBindVertexArray imported
1>main.obj : warning LNK4049: locally defined symbol ___glewGenVertexArrays imported
1>main.obj : error LNK2019: unresolved external symbol "unsigned int __cdecl LoadShaders(struct ShaderInfo)" (?LoadShaders@@YAIUShaderInfo@@@Z) referenced in function "void __cdecl init(void)" (?init@@YAXXZ)
1>C:\Users\Callum\documents\visual studio 2012\Projects\sarpg\Debug\sarpg.exe : fatal error LNK1120: 1 unresolved externals
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

main.cpp

#include <iostream>
//#include <GL/glew.h>
//#include <GL/glut.h>
#include "LoadShader.h"
#include "vgl.h"
//#pragma comment( lib, "C://Libs/GLEW/glew-1.9.0/lib/glew32.lib" )
#define BUFFER_OFFSET(offset) ((void *)(offset))

enum VAO_IDs {Triangles, NumVAOs};
enum Buffer_IDs {ArrayBuffer, NumBuffers};
enum Attrib_IDs{vPosition = 0};

GLuint VAOs[NumVAOs];
GLuint Buffers[NumBuffers];

const GLuint NumVertices = 6;

void init(void) {
    glGenVertexArrays(NumVAOs, VAOs);
    glBindVertexArray(VAOs[Triangles]);

    GLfloat vertices[NumVertices][2] = {
        {-0.90, -0.90},
        {0.85, -0.90},
        {-0.90, 0.85},
        {0.90, -0.85},
        {0.90, 0.90},
        {-0.85, 0.90}
    };

    glGenBuffers(NumBuffers, Buffers);
    glBindBuffer(GL_ARRAY_BUFFER, Buffers[ArrayBuffer]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    ShaderInfo shaders[] = {
        {GL_VERTEX_SHADER, "triangles.vert"},
        {GL_FRAGMENT_SHADER, "triangles.frag"},
        {GL_NONE, NULL}};

    GLuint program = LoadShaders(*shaders);
    glUseProgram(program);
}

void display(void){

    glClear(GL_COLOR_BUFFER_BIT);

    glBindVertexArray(VAOs[Triangles]);
    glDrawArrays(GL_TRIANGLES, 0, NumVertices);

    glFlush();
}

int main(int argc, char** argv){
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGBA);
    glutInitWindowSize(512, 512);
    glutInitContextVersion(4, 3);
    glutInitContextProfile(GLUT_CORE_PROFILE);
    glutCreateWindow(argv[0]);

    if(glewInit()) {
        cerr << "Unable to init GLEW ... exiting" <<endl;
        exit(EXIT_FAILURE);
    }

    init();
    glutDisplayFunc(display);
    glutMainLoop();
}

负载着色器.cpp

//////////////////////////////////////////////////////////////////////////////
//
//  --- LoadShaders.cxx ---
//
//////////////////////////////////////////////////////////////////////////////

#include <cstdlib>
#include <iostream>

#define GLEW_STATIC
#include <GL/glew.h>
#include "LoadShaders.h"

#ifdef __cplusplus
extern "C" {
#endif // __cplusplus

//----------------------------------------------------------------------------

static const GLchar*
ReadShader( const char* filename )
{
#ifdef WIN32
    FILE* infile;
    fopen_s( &infile, filename, "rb" );
#else
    FILE* infile = fopen( filename, "rb" );
#endif // WIN32

    if ( !infile ) {
#ifdef _DEBUG
        std::cerr << "Unable to open file '" << filename << "'" << std::endl;
#endif /* DEBUG */
        return NULL;
    }

    fseek( infile, 0, SEEK_END );
    int len = ftell( infile );
    fseek( infile, 0, SEEK_SET );

    GLchar* source = new GLchar[len+1];

    fread( source, 1, len, infile );
    fclose( infile );

    source[len] = 0;

    return const_cast<const GLchar*>(source);
}

//----------------------------------------------------------------------------

GLuint
LoadShaders( ShaderInfo* shaders )
{
    if ( shaders == NULL ) { return 0; }

    GLuint program = glCreateProgram();

    ShaderInfo* entry = shaders;
    while ( entry->type != GL_NONE ) {
        GLuint shader = glCreateShader( entry->type );

        entry->shader = shader;

        const GLchar* source = ReadShader( entry->filename );
        if ( source == NULL ) {
            for ( entry = shaders; entry->type != GL_NONE; ++entry ) {
                glDeleteShader( entry->shader );
                entry->shader = 0;
            }

            return 0;
        }

        glShaderSource( shader, 1, &source, NULL );
        delete [] source;

        glCompileShader( shader );

        GLint compiled;
        glGetShaderiv( shader, GL_COMPILE_STATUS, &compiled );
        if ( !compiled ) {
#ifdef _DEBUG
            GLsizei len;
            glGetShaderiv( shader, GL_INFO_LOG_LENGTH, &len );

            GLchar* log = new GLchar[len+1];
            glGetShaderInfoLog( shader, len, &len, log );
            std::cerr << "Shader compilation failed: " << log << std::endl;
            delete [] log;
#endif /* DEBUG */

            return 0;
        }

        glAttachShader( program, shader );

        ++entry;
    }

#ifdef GL_VERSION_4_1
    if ( GLEW_VERSION_4_1 ) {
        // glProgramParameteri( program, GL_PROGRAM_SEPARABLE, GL_TRUE );
    }
#endif /* GL_VERSION_4_1 */

    glLinkProgram( program );

    GLint linked;
    glGetProgramiv( program, GL_LINK_STATUS, &linked );
    if ( !linked ) {
#ifdef _DEBUG
        GLsizei len;
        glGetProgramiv( program, GL_INFO_LOG_LENGTH, &len );

        GLchar* log = new GLchar[len+1];
        glGetProgramInfoLog( program, len, &len, log );
        std::cerr << "Shader linking failed: " << log << std::endl;
        delete [] log;
#endif /* DEBUG */

        for ( entry = shaders; entry->type != GL_NONE; ++entry ) {
            glDeleteShader( entry->shader );
            entry->shader = 0;
        }

        return 0;
    }

    return program;
}

//----------------------------------------------------------------------------
#ifdef __cplusplus
}
#endif // __cplusplus

负载着色器.h

//////////////////////////////////////////////////////////////////////////////
//
//  --- LoadShaders.h ---
//
//////////////////////////////////////////////////////////////////////////////

#ifndef __LOAD_SHADERS_H__
#define __LOAD_SHADERS_H__

#include <GL/gl.h>

#ifdef __cplusplus
extern "C" {
#endif  // __cplusplus

//----------------------------------------------------------------------------
//
//  LoadShaders() takes an array of ShaderFile structures, each of which
//    contains the type of the shader, and a pointer a C-style character
//    string (i.e., a NULL-terminated array of characters) containing the
//    entire shader source.
//
//  The array of structures is terminated by a final Shader with the
//    "type" field set to GL_NONE.
//
//  LoadShaders() returns the shader program value (as returned by
//    glCreateProgram()) on success, or zero on failure. 
//

typedef struct {
    GLenum       type;
    const char*  filename;
    GLuint       shader;
} ShaderInfo;

GLuint LoadShaders( ShaderInfo* );

//----------------------------------------------------------------------------

#ifdef __cplusplus
};
#endif // __cplusplus

#endif // __LOAD_SHADERS_H__

vgl.h

#ifndef __VGL_H__
#define __VGL_H__

// #define USE_GL3W

#ifdef USE_GL3W

#include <GL3/gl3.h>
#include <GL3/gl3w.h>

#else

#define GLEW_STATIC

#include <GL/glew.h>

#ifdef _MSC_VER
#  ifdef _DEBUG
#    if (_MSC_VER >= 1600)
#      pragma comment (lib, "glew_static_vs2010_d.lib")
#    else
#      pragma comment (lib, "glew_static_d.lib")
#    endif
#  else
#    if (_MSC_VER >= 1600)
#      pragma comment (lib, "glew_static_vs2010.lib")
#    else
#      pragma comment (lib, "glew_static.lib")
#    endif
#  endif
#endif

#endif

#define FREEGLUT_STATIC

#include <GL/freeglut.h>

#ifdef _MSC_VER
#  ifdef _DEBUG
#    if (_MSC_VER >= 1600)
#      pragma comment (lib, "freeglut_static_vs2010_d.lib")
#    else
#      pragma comment (lib, "freeglut_static_d.lib")
#    endif
#  else
#    if (_MSC_VER >= 1600)
#      pragma comment (lib, "freeglut_static_vs2010.lib")
#    else
#      pragma comment (lib, "freeglut_static.lib")
#    endif
#  endif
#endif

#define BUFFER_OFFSET(x)  ((const void*) (x))

#endif /* __VGL_H__ */

(P.S. 是的，我确实记得链接库(我想))

Answer 1

缺少 LoadShaders(struct ShaderInfo) 符号的错误表明您的 main.cpp 包含定义不同 LoadShaders 的内容原型(prototype)比我在您的 LoadShaders.h 中看到的要多。奇怪的是，也许是打字错误，您的 main.cpp 包含 LoadShader.h(缺少“s”)，但实际 header 称为 LoadShaders.h 。也许巧合的是，LoadShader.h 位于某个地方，具有不同的函数原型(prototype)。