c++ - 顶点/索引缓冲区与 OpenGL 3.3 混淆

Question

我正在尝试使用 OpenGL 3.3 渲染 3D 立方体。我的代码大致基于 Chapter 4 of the OpenGL book 中的代码

这是我的代码:

// Attempt to make a cube in OpenGL 3.3, using GLEW and GLFW
#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <cmath>
// Include GLEW (openGL Extension Wrangler)
#define GLEW_STATIC
#include <GL/glew.h>
// Include GLFW (openGL FrameWork)
#include <GL/glfw.h>
// Define this helper macro to get an array position
#define BUFFER_OFFSET(i) ((char *)NULL + (i))

static const double PI = 3.14159265358979323846;

float radians(float inDeg)
{
    return inDeg * PI/180.0 ;
}

struct Vertex
{ // 64 bytes = 16 x 4 bytes per float
    GLfloat x, y, z ;         // position coordinates
    GLfloat nx, ny, nz ;      // normal coordinates
    GLfloat r, g, b, a ;      // color coordinates for vertex shading
    GLfloat s0, t0 ;          // s and t are the standard texture coordinates
    GLfloat s1, t1 ;          // (just used as padding)
    GLfloat s2, t2 ;          // (just used as padding)
} ;
// Vertex Attributes
GLuint      vertexSize       = sizeof( Vertex ) ;
GLuint      positionOffset   = 0 ;
GLuint      colorOffset      = 24 ;
// Vertex Data - stored dynamically, see BuildCube()
Vertex     *vertexData ;
GLuint     *indexData  ;
GLuint      vertexDataLength = 8  ;
GLuint      indexDataLength  = 36 ;

struct Matrix
{ // 64 bytes = 16 x 4 bytes per float
    GLfloat m[16] ;
} ;
// Matrix Data
Matrix      ModelMatrix ;
Matrix      ViewMatrix  ;
Matrix      ProjMatrix  ;

Matrix IdentityMatrix(void)
{   // set the diagonal values to one
    Matrix out ;
    out.m[0]  =  1.0 ; out.m[1]  =  0.0 ; out.m[2]  =  0.0 ; out.m[3]  =  0.0 ;
    out.m[4]  =  0.0 ; out.m[5]  =  1.0 ; out.m[6]  =  0.0 ; out.m[7]  =  0.0 ;
    out.m[8]  =  0.0 ; out.m[9]  =  0.0 ; out.m[10] =  1.0 ; out.m[11] =  0.0 ;
    out.m[12] =  0.0 ; out.m[13] =  0.0 ; out.m[14] =  0.0 ; out.m[15] =  1.0 ;
    return out ;
}

Matrix ZeroMatrix(void)
{   // set all values to zero
    Matrix out ;
    out.m[0]  =  0.0 ; out.m[1]  =  0.0 ; out.m[2]  =  0.0 ; out.m[3]  =  0.0 ;
    out.m[4]  =  0.0 ; out.m[5]  =  0.0 ; out.m[6]  =  0.0 ; out.m[7]  =  0.0 ;
    out.m[8]  =  0.0 ; out.m[9]  =  0.0 ; out.m[10] =  0.0 ; out.m[11] =  0.0 ;
    out.m[12] =  0.0 ; out.m[13] =  0.0 ; out.m[14] =  0.0 ; out.m[15] =  0.0 ;
    return out ;
}

Matrix Multiply(const Matrix *m1, const Matrix *m2)
{
    // Since these are note REALLY matrixes, we can get away with a shortcut
    Matrix out = IdentityMatrix() ;
    GLuint row, column, row_offset ;
    for (row = 0; row < 4; row++)
    {
        row_offset = row * 4 ;
        for (column = 0; column < 4; column++)
        {
            out.m[row_offset + column] =
            (m1->m[row_offset + 0] * m2->m[column + 0]) +
            (m1->m[row_offset + 1] * m2->m[column + 4]) +
            (m1->m[row_offset + 2] * m2->m[column + 8]) +
            (m1->m[row_offset + 3] * m2->m[column + 12]) ;
        }
    }
    return out ;
}

void Translate(Matrix &inMat, GLfloat dx, GLfloat dy, GLfloat dz)
{
    Matrix TM = IdentityMatrix() ;
    TM.m[3]  =  dx ;
    TM.m[7]  =  dy ;
    TM.m[11] =  dz ;
    inMat = Multiply(&inMat, &TM) ;
}

void Rotate(Matrix &inMat, GLfloat xAng, GLfloat yAng, GLfloat zAng)
{   // rotates a vector or point around the origin at the specified angles
    // create the half-angle values in radians
    GLfloat rad_x_ang = radians(xAng)/2.0 * -1.0 ;      // multiply by -1 to make the rotation right-handed
    GLfloat rad_y_ang = radians(yAng)/2.0        ;
    GLfloat rad_z_ang = radians(zAng)/2.0 ;      // multiply by -1 to make the rotation right-handed
    // compute sin and cos values, so they're not repeated a LOT
    GLfloat cosX = cos(rad_x_ang) ;
    GLfloat sinX = sin(rad_x_ang) ;
    GLfloat cosY = cos(rad_y_ang) ;
    GLfloat sinY = sin(rad_y_ang) ;
    GLfloat cosZ = cos(rad_z_ang) ;
    GLfloat sinZ = sin(rad_z_ang) ;
    // create quaternion vector: Q
    GLfloat q0 = cosZ * cosY * cosX + sinZ * sinY * sinX ;
    GLfloat q1 = sinZ * cosY * cosX - cosZ * sinY * sinX ;
    GLfloat q2 = cosZ * sinY * cosX + sinZ * cosY * sinX ;
    GLfloat q3 = cosZ * cosY * sinX - sinZ * sinY * cosX ;
    // create rotation matrix
    Matrix RM ;
    RM.m[0]  = q0*q0+q1*q1+q2*q2+q3*q3 ; RM.m[1]  = 0.0                     ; RM.m[2]  = 0.0                     ; RM.m[3]  = 0.0                     ;
    RM.m[4]  = 0.0                     ; RM.m[5]  = q0*q0-q1*q1-q2*q2+q3*q3 ; RM.m[6]  = 2*q2*q3 - 2*q0*q1       ; RM.m[7]  = 2*q1*q3 + 2*q0*q2       ;
    RM.m[8]  = 0.0                     ; RM.m[9]  = 2*q2*q3 + 2*q0*q1       ; RM.m[10] = q0*q0-q1*q1+q2*q2-q3*q3 ; RM.m[11] = 2*q1*q2 - 2*q0*q3       ;
    RM.m[12] = 0.0                     ; RM.m[13] = 2*q1*q3 - 2*q0*q2       ; RM.m[14] = 2*q1*q2 + 2*q0*q3       ; RM.m[15] = q0*q0+q1*q1-q2*q2-q3*q3 ;
    // multiply the new rotational matrix with the current incoming matrix
    inMat = Multiply(&inMat, &RM) ;
}

const GLchar* VertexShader =
{
    "#version 330\n"\
    "attribute vec3 in_Position;\n"\
    "attribute vec4 in_Color;\n"\
    "uniform   mat4 ModelMatrix;\n"\
    "uniform   mat4 ViewMatrix;\n"\
    "uniform   mat4 ProjMatrix ;\n"\
    "out       vec4 ex_Color;\n"\
    "void main(void)\n"\
    "{\n"\
    "   gl_Position = (ProjMatrix * ViewMatrix * ModelMatrix) * vec4(in_Position, 1.0);\n"\
    "   ex_Color    = in_Color;\n"\
    "}\n"
};

const GLchar* FragmentShader =
{
    "#version 330\n"\
    "in  vec4 ex_Color ;\n"\
    "out vec4 out_Color ;\n"\
    "void main(void)\n"\
    "{\n"\
    "   out_Color = ex_Color ;\n"\
    "}\n"
};

// Shader Attribute IDs
GLuint      attribute_in_Position ;
GLuint      attribute_in_Color ;
GLuint      uniform_ModelMatrix ;
GLuint      uniform_ViewMatrix ;
GLuint      uniform_ProjMatrix ;
// OpenGL Object IDs
GLuint      VertShaderID ;
GLuint      FragShaderID ;
GLuint      GLSLProgID ;
GLuint      vaoID ;
GLuint      vboID ;
GLuint      iboID ;

// Forward declare functions
void        BuildCube(void) ;
void        CreateShaders(void) ;
void        DestroyShaders(void) ;
void        InitStuff(void) ;
bool        DrawStuff(int) ;
void        KillStuff(void) ;

void BuildCube(void)
{
    vertexData = new Vertex[8] ;   // create a dynamic memory array of 8 vertices
    indexData  = new GLuint[36] ;
    // specify only 8 vertices (ignore texture and normals for now)
    vertexData[0].x  =  0.5 ; vertexData[0].y  =  0.5 ; vertexData[0].z  =  0.5 ;
    vertexData[1].x  = -0.5 ; vertexData[1].y  =  0.5 ; vertexData[1].z  =  0.5 ;
    vertexData[2].x  = -0.5 ; vertexData[2].y  = -0.5 ; vertexData[2].z  =  0.5 ;
    vertexData[3].x  =  0.5 ; vertexData[3].y  = -0.5 ; vertexData[3].z  =  0.5 ;
    vertexData[4].x  =  0.5 ; vertexData[4].y  =  0.5 ; vertexData[4].z  = -0.5 ;
    vertexData[5].x  = -0.5 ; vertexData[5].y  =  0.5 ; vertexData[5].z  = -0.5 ;
    vertexData[6].x  = -0.5 ; vertexData[6].y  = -0.5 ; vertexData[6].z  = -0.5 ;
    vertexData[7].x  =  0.5 ; vertexData[7].y  = -0.5 ; vertexData[7].z  = -0.5 ;
    // specify all triangles
    indexData[0]  = 0 ; indexData[1]  = 1 ; indexData[2]  = 2 ;  // top
    indexData[3]  = 2 ; indexData[4]  = 3 ; indexData[5]  = 0 ;
    indexData[6]  = 4 ; indexData[7]  = 6 ; indexData[8]  = 5 ;  // bottom
    indexData[9]  = 6 ; indexData[10] = 4 ; indexData[11] = 7 ;
    indexData[12] = 2 ; indexData[13] = 1 ; indexData[14] = 5 ;  // left
    indexData[15] = 5 ; indexData[16] = 6 ; indexData[17] = 2 ;
    indexData[18] = 0 ; indexData[19] = 3 ; indexData[20] = 4 ;  // right
    indexData[21] = 3 ; indexData[22] = 7 ; indexData[23] = 4 ;
    indexData[24] = 1 ; indexData[25] = 0 ; indexData[26] = 5 ;  // front
    indexData[27] = 0 ; indexData[28] = 4 ; indexData[29] = 5 ;
    indexData[30] = 3 ; indexData[31] = 2 ; indexData[32] = 6 ;  // back
    indexData[33] = 6 ; indexData[34] = 7 ; indexData[35] = 3 ;
    // specify the colors
    for (unsigned int ii = 0; ii < 8; ii++)
    {   //
        vertexData[ii].r =  vertexData[ii].x + 0.5 ;
        vertexData[ii].g =  vertexData[ii].y + 0.5 ;
        vertexData[ii].b =  vertexData[ii].z + 0.5 ;
        vertexData[ii].a =  1.0 ;
    }
    // end BuildCube()
}

void CreateShaders(void)
{
    GLenum ErrorCheckValue = glGetError();
    // establish vertex shader
    VertShaderID = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(VertShaderID, 1, &VertexShader, NULL);
    glCompileShader(VertShaderID);
    // establish fragment shader
    FragShaderID = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(FragShaderID, 1, &FragmentShader, NULL);
    glCompileShader(FragShaderID);
    // set the GLSL program ID
    GLSLProgID = glCreateProgram();
        // link the vertex and fragment shaders
        glAttachShader(GLSLProgID, VertShaderID);
        glAttachShader(GLSLProgID, FragShaderID);
    glLinkProgram(GLSLProgID);
    glUseProgram(GLSLProgID);
    // check for errors before continuing
    ErrorCheckValue = glGetError();
    if (ErrorCheckValue != GL_NO_ERROR)
    {
        fprintf(
            stderr,
            "ERROR: Could not create the shaders: %s \n",
            gluErrorString(ErrorCheckValue)
        );
        exit(-1);
    }
}

void DestroyShaders(void)
{
    if (!glfwGetWindowParam(GLFW_OPENED)) { return ; }
    GLenum ErrorCheckValue = glGetError();
    glUseProgram(0);
    glDetachShader(GLSLProgID, VertShaderID);
    glDetachShader(GLSLProgID, FragShaderID);
    glDeleteShader(FragShaderID);
    glDeleteShader(VertShaderID);
    glDeleteProgram(GLSLProgID);
    // check for errors last
    ErrorCheckValue = glGetError();
    if (ErrorCheckValue != GL_NO_ERROR)
    {
        fprintf(
            stderr,
            "ERROR: Could not destroy the shaders: %s \n",
            gluErrorString(ErrorCheckValue)
        ) ;
        exit(-1) ;
    }
}

void InitStuff(void)
{
    // Initialise GLFW extension
    if( !glfwInit() )
    {   // If the extension failed to initialize, then error out and leave.
        fprintf( stderr, "Failed to initialize GLFW\n" ) ;
        return ;
    }
    // Establish OpenGL version 3.3
    glfwOpenWindowHint(GLFW_FSAA_SAMPLES, 4);
    glfwOpenWindowHint(GLFW_OPENGL_VERSION_MAJOR, 3);
    glfwOpenWindowHint(GLFW_OPENGL_VERSION_MINOR, 3);
    glfwOpenWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
    glfwOpenWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_COMPAT_PROFILE);    // This compensates for the bug in GLEW
    // Open a window and create its OpenGL context
    if( !glfwOpenWindow( 512, 512, 0,0,0,0, 0,0, GLFW_WINDOW ) )
    {
        fprintf( stderr, "Failed to open GLFW window.\n" ) ;
        glfwTerminate() ;
        exit(-1) ;
    }
    // Initialize GLEW extension
    if (glewInit() != GLEW_OK)
    {
        fprintf(stderr, "Failed to initialize GLEW\n") ;
        exit(-1) ;
    }
    // Set the title on the upper left of the window
    glfwSetWindowTitle("Test Window") ;
    // Ensure we can capture the escape key being pressed below
    glfwEnable( GLFW_STICKY_KEYS ) ;
    // Clear Screen And Depth Buffer
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT) ;

    // Establish the matrixes
    int width, height ;
    glfwGetWindowSize( &width, &height );       // assess window size
    height = height > 0 ? height : 1;           // avoid div/0 error
    // calculate the projection matrix values
    GLfloat     fov_y          = 45.0 ;
    GLfloat     aspect_ratio   = (GLfloat) width / (GLfloat) height ;
    GLfloat     near_plane     = 1.0 ;
    GLfloat     far_plane      = 100.0 ;
    GLfloat     y_scale        = 1.0 / tan( radians(fov_y / 2.0) ) ;
    GLfloat     x_scale        = y_scale / aspect_ratio ;
    GLfloat     frustum_length = far_plane - near_plane ;
    ProjMatrix = ZeroMatrix() ;
    ProjMatrix.m[0]  =   x_scale ;
    ProjMatrix.m[5]  =   y_scale ;
    ProjMatrix.m[10] =  -((far_plane + near_plane) / frustum_length) ;
    ProjMatrix.m[11] =  -1.0 ;
    ProjMatrix.m[14] =  -((2.0 * near_plane * far_plane) / frustum_length) ;

    // Establish the model and view matrixes as identity matrixes
    ModelMatrix = IdentityMatrix() ;
    ViewMatrix = IdentityMatrix() ;

    Translate(ViewMatrix, 0.0, 0.0, -2.0) ;
    // Creat the error enumeration
    GLenum ErrorCheckValue = glGetError();

    // Create the vertex and fragment shaders
    CreateShaders() ;
    // Bind the vertex shader attributes to their IDs
    attribute_in_Position =  glGetAttribLocation(GLSLProgID, "in_Position") ;
    attribute_in_Color    =  glGetAttribLocation(GLSLProgID, "in_Color"   ) ;
    uniform_ModelMatrix   = glGetUniformLocation(GLSLProgID, "ModelMatrix") ;
    uniform_ViewMatrix    = glGetUniformLocation(GLSLProgID, "ViewMatrix" ) ;
    uniform_ProjMatrix    = glGetUniformLocation(GLSLProgID, "ProjMatrix" ) ;

    // upload the projection matrix data to the GPU
    glUniformMatrix4fv(uniform_ModelMatrix, 1, GL_TRUE, ModelMatrix.m);
    glUniformMatrix4fv(uniform_ViewMatrix , 1, GL_TRUE, ViewMatrix.m );
    glUniformMatrix4fv(uniform_ProjMatrix , 1, GL_TRUE, ProjMatrix.m );

    // Build the Cube Geometry
    BuildCube() ;

    // Initialize the Vertex Buffer Object in OpenGL
    glGenBuffers(1, &vboID);
    glBindBuffer(GL_ARRAY_BUFFER, vboID);
    glBufferData(GL_ARRAY_BUFFER, vertexSize * vertexDataLength, NULL, GL_STATIC_DRAW);
    glBufferSubData(GL_ARRAY_BUFFER, 0, vertexSize * vertexDataLength, vertexData);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    // Initialize the Index Buffer Object in OpenGL
    glGenBuffers(1, &iboID);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, iboID);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLuint) * indexDataLength, NULL, GL_STATIC_DRAW);
    glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, sizeof(GLuint) * indexDataLength, indexData);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);



    // Check for errors, then done
    ErrorCheckValue = glGetError() ;
    if (ErrorCheckValue != GL_NO_ERROR)
    {
        fprintf(
            stderr,
            "ERROR: Could not complete initialization: %s \n",
            gluErrorString(ErrorCheckValue)
        ) ;
        exit(-1) ;
    }
    // end InitStuff()
}

bool DrawStuff(int frame)
{
    int width, height ;
    glfwGetWindowSize( &width, &height ) ;   // First, re-assess the window size
    height = height > 0 ? height : 1 ;       // avoid div/0 error
    // for now, vary the background color so we know it's updating
    GLfloat phase_offset = 125.0f ;
    GLfloat speed_mult   = 0.01f ;
    GLfloat bgColorR = 0.5f * ( sin( (frame-0)*speed_mult ) + 1.0f );
    GLfloat bgColorG = 0.5f * ( sin( (frame-phase_offset)*speed_mult ) + 1.0f );
    GLfloat bgColorB = 0.5f * ( sin( (frame-2*phase_offset)*speed_mult ) + 1.0f );
    glClearColor( bgColorR, bgColorG, bgColorB, 0.0f );
    // Handle projection stuff
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    glViewport( 0, 0, width, height );
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    //
    GLenum ErrorCheckValue = glGetError();

    glEnable(GL_DEPTH_TEST) ;
    glDepthFunc(GL_LESS) ;
    glEnable(GL_CULL_FACE) ;
    glCullFace(GL_BACK) ;
    glFrontFace(GL_CCW) ;

    ErrorCheckValue = glGetError();
    if (ErrorCheckValue != GL_NO_ERROR)
    {
        fprintf(
            stderr,
            "ERROR: Could not set OpenGL culling options: %s \n",
            gluErrorString(ErrorCheckValue)
        ) ;
        exit(-1) ;
    }


    // switch to model view mode
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();

    // Assume I have multiple VBOs, but streamline for only one for now
    glPushMatrix() ;

        // re-bind the VBO data into the buffer
        glBindBuffer(GL_ARRAY_BUFFER, vboID) ;
        glVertexAttribPointer(attribute_in_Color, 4, GL_FLOAT, GL_FALSE, vertexSize, BUFFER_OFFSET(colorOffset)) ;
        glEnableVertexAttribArray(attribute_in_Color) ;

        glBindBuffer(GL_ARRAY_BUFFER, vboID) ;
        glVertexAttribPointer(attribute_in_Position, 3, GL_FLOAT, GL_FALSE, vertexSize, BUFFER_OFFSET(positionOffset)) ;
        glEnableVertexAttribArray(attribute_in_Position) ;

        // bind the indexes of the vertices to the buffer
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, iboID) ;

        Rotate(ModelMatrix, 0.0, 0.0, 0.5) ;
        glUniformMatrix4fv(uniform_ModelMatrix, 1, GL_TRUE, ModelMatrix.m);

        ErrorCheckValue = glGetError();
        if (ErrorCheckValue != GL_NO_ERROR)
        {
            fprintf(
                stderr,
                "ERROR: Could not prep for draw: %s \n",
                gluErrorString(ErrorCheckValue)
            ) ;
            exit(-1) ;
        }

        glDrawArrays(GL_TRIANGLES, 0, indexDataLength);

        glDisableVertexAttribArray(attribute_in_Color) ;
        glDisableVertexAttribArray(attribute_in_Position) ;
        glBindBuffer(GL_ARRAY_BUFFER, 0) ;
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0) ;

    glPopMatrix();
    // lastly, swap buffers, then return the status
    glfwSwapBuffers();
    return !glfwGetKey(GLFW_KEY_ESC) && glfwGetWindowParam(GLFW_OPENED);
}

void KillStuff(void)
{
    DestroyShaders();
    glfwTerminate();
}

int main()
{
    int     frame = 0 ;
    bool    running = true;
    InitStuff() ;
    while(running)
    {
        frame++;
        running = DrawStuff(frame) ;
    }
    KillStuff() ;
    return 0;
}

结果是大约 3 个未真正遵循正确索引的部分形成的三角形。我认为问题出在索引缓冲区中，但我真的可以使用一些帮助来理解我是否错误地使用了索引和顶点缓冲区。我对自己做错了什么感到很困惑。

Answer 1

glDrawArrays 不读取顶点索引，它只是按顺序从 GL_ARRAY_BUFFER 中绘制顶点。如果要使用索引缓冲区，则需要改用 glDrawElements。

以后也请尽量只贴出相关的代码部分。如果您不确定某些内容是否相关，则在包含方面犯错，但如果不深入研究矩阵操作函数、着色器链接函数等，很难找到重要的内容。如果您发表简洁的文章，您会得到更好的答案代码。