c++ - Open_GL 中的透视问题

Question

有人可以解释一下我的代码有什么问题吗？当我尝试运行它时，我得到一个黑色窗口，但如果我没有像在第 31 行中那样设置透视矩阵，我会在窗口上绘制正确的实体(金字塔)。这是代码的主要部分。在顶点着色器中，我只是将模型、 View 和投影定义为统一的 4x4 矩阵，并将它们乘以顶点的位置，并将顶点的颜色传递给片段着色器。我认为问题不在这些文件中，但如果您需要它们，我会发布它们。

#include <iostream>
#include <GL/glew.h>
#include <GL/freeglut.h>
#include <string>
#include <fstream>
#include <sstream> 
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>

using namespace std;

GLuint IBO, VBO, gModelLocation, gViewLocation, gProjectionLocation;

#define WINDOW_WIDTH 800
#define WINDOW_HEIGHT 600 

const char* VSfileName = "vertex.vs";
const char* FSfileName = "fragment.fs";

void RenderSceneCB()
{
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

    glm::mat4 model;
    model = glm::rotate( model, 0.0f, glm::normalize( glm::vec3( 1.0, 0.0, 0.0 ) ) );

    glm::mat4 view;
    view = glm::translate( view, glm::vec3( 0.0f, 0.0f, 0.0f ) );

    glm::mat4 projection;
    projection = glm::perspective( 90.0f, float( WINDOW_WIDTH ) / float( WINDOW_HEIGHT ), 0.1f, 100.0f );

    glUniformMatrix4fv( gModelLocation, 1, GL_FALSE, &model[ 0 ][ 0 ] );
    glUniformMatrix4fv( gViewLocation, 1, GL_FALSE, &view[ 0 ][ 0 ] );
    glUniformMatrix4fv( gProjectionLocation, 1, GL_FALSE, glm::value_ptr( projection ) );

    glBindBuffer( GL_ARRAY_BUFFER, VBO );
    glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, IBO );

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

    glVertexAttribPointer( 1, 3, GL_FLOAT, GL_FALSE, 0, (GLvoid*)( 15 * sizeof( GLfloat ) ) );
    glEnableVertexAttribArray( 1 );

    glDrawElements( GL_TRIANGLES, 12, GL_UNSIGNED_INT, 0 );
    //glDrawArrays(GL_TRIANGLES, 0, 3);

    glDisableVertexAttribArray( 1 );
    glDisableVertexAttribArray( 0 );

    glutSwapBuffers();
}

void InizializeGlutCallBacks()
{
    glutDisplayFunc( RenderSceneCB );
    glutIdleFunc( RenderSceneCB );
}

void InizializeVertices()
{
    GLfloat Vertices[ 9 ][ 3 ]
    {
        { -0.5f, 0.5f, 0.0f},
        { 0.5f, -0.5f, 0.0f },
        { 0.5f, 0.5f, 0.0f},
        { -0.5f, -0.5f, 0.0f },
        { 0.0f, 0.0f, 1.0f},
        { 1.0f, 0.0f, 0.0f},
        { 0.0f, 1.0f, 0.0f },
        { 0.0f, 0.0f, 1.0f },
        { 1.0f, 1.0f, 1.0f}
    };
    GLint Indices[ 12 ]
    {
        0,2,4,0,3,4,1,2,4,1,3,4
    };

    glGenBuffers( 1, &VBO );
    glGenBuffers( 1, &IBO );

    glBindBuffer( GL_ARRAY_BUFFER, VBO );
    glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, IBO );

    glBufferData( GL_ARRAY_BUFFER, sizeof( Vertices ), Vertices, GL_STATIC_DRAW );
    glBufferData( GL_ELEMENT_ARRAY_BUFFER, sizeof( Indices ), Indices, GL_STATIC_DRAW );

}

void AddShader( GLuint ShaderProgram, const char* ShaderSource, GLenum ShaderType )
{

    GLuint ShaderObj = glCreateShader( ShaderType );
    if( ShaderObj == 0 )
    {
        fprintf( stderr, "Error creating Shader Object %d \n", ShaderType );
    }

    const GLchar* p[ 1 ];
    p[ 0 ] = ShaderSource;

    GLint Lengths[ 1 ];
    Lengths[ 0 ] = strlen( p[ 0 ] );

    glShaderSource( ShaderObj, 1, p, Lengths );

    glCompileShader( ShaderObj );
    GLint success;
    glGetShaderiv( ShaderObj, GL_COMPILE_STATUS, &success );
    if( !success )
    {
        GLchar InfoLog[ 1024 ];
        glGetShaderInfoLog( ShaderObj, 1024, NULL, InfoLog );
        fprintf( stderr, "Error Compiling Shader %d: '%s' \n", ShaderType, InfoLog );
    }

    glAttachShader( ShaderProgram, ShaderObj );
}

void CompileShaders()
{
    GLuint ShaderProgram = glCreateProgram();
    if( ShaderProgram == 0 )
    {
        fprintf( stderr, "Error creating Shader Program \n" );
    }

    string vs, fs;

    ifstream VertexFile;
    ifstream FragmentFile;

    VertexFile.open( VSfileName );
    if( !VertexFile )
    {
        std::cout << "Error in opening vertex.vs \n";
        exit( 1 );
    }
    FragmentFile.open( FSfileName );
    if( !FragmentFile )
    {
        std::cout << "Error in opening fragment.fs \n";
        exit( 1 );
    }

    stringstream VertexStream;
    stringstream FragmentStream;

    VertexStream << VertexFile.rdbuf();
    FragmentStream << FragmentFile.rdbuf();

    vs = VertexStream.str();
    fs = FragmentStream.str();

    AddShader( ShaderProgram, vs.c_str(), GL_VERTEX_SHADER );
    AddShader( ShaderProgram, fs.c_str(), GL_FRAGMENT_SHADER );

    glLinkProgram( ShaderProgram );
    GLint success;
    glGetProgramiv( ShaderProgram, GL_LINK_STATUS, &success );
    if( !success )
    {
        GLchar InfoLog[ 1024 ];
        glGetProgramInfoLog( ShaderProgram, 1024, NULL, InfoLog );
        fprintf( stderr, "Error in linking Shader '%s' \n", InfoLog );
    }

    glValidateProgram( ShaderProgram );
    glGetProgramiv( ShaderProgram, GL_VALIDATE_STATUS, &success );
    if( !success )
    {
        GLchar InfoLog[ 1024 ];
        glGetProgramInfoLog( ShaderProgram, 1024, NULL, InfoLog );
        fprintf( stderr, "Error in linking Shader '%s' \n", InfoLog );
    }

    //gScaleLocation = glGetUniformLocation(ShaderProgram, "gScale");
    gModelLocation = glGetUniformLocation( ShaderProgram, "gModel" );
    gViewLocation = glGetUniformLocation( ShaderProgram, "gView" );
    gProjectionLocation = glGetUniformLocation( ShaderProgram, "gProjection" );
    glUseProgram( ShaderProgram );
}

int main( int argc, char **argv )
{
    glutInit( &argc, argv );
    glutInitDisplayMode( GLUT_DOUBLE | GLUT_RGBA );
    glutInitWindowSize( WINDOW_WIDTH, WINDOW_HEIGHT );
    glutInitWindowPosition( 100, 100 );
    glutCreateWindow( "Hello World" );

    InizializeGlutCallBacks();

    glClearColor( 0.0f, 0.0f, 0.0f, 0.0f );

    GLenum res = glewInit();
    if( res != GLEW_OK )
    {
        std::cout << "Error, check please \n";
    }

    glViewport( 0, 0, WINDOW_WIDTH, WINDOW_HEIGHT );

    glEnable( GL_DEPTH_TEST );

    // enable alpha support
    glEnable( GL_BLEND );
    glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );

    InizializeVertices();

    CompileShaders();

    glutMainLoop();

    system( "pause" );

    return 0;
}

Answer 1

首先你应该初始化所有的矩阵(见 glm returning nan on simple translate ):

glm::mat4 model(1.0f);
glm::mat4 view(1.0f);
glm::mat4 projection(1.0f);

几何体必须在裁剪空间中。当您设置投影时，您可以定义 0.1 的近平面和 100.0 的远平面。这两个值定义近和远裁剪平面。
这意味着您只能“看到”Z 分量在 [0.1, 100.0] 范围内的几何图形。

设置 View 矩阵，解决您的问题。

glm::mat4 view(1.0f);
view = glm::translate( view, glm::vec3( 0.0f, 0.0f, -1.0f ) );

更远:查看GLM glm::perspective , version 0.9.8 的文档:

LM_FUNC_DECL tmat4x4<T, defaultp> glm::perspective(T fovy, T aspect, T near, T far)

Creates a matrix for a symetric perspective-view frustum based on the default handedness.

Parameters
fovy Specifies the field of view angle in the y direction. Expressed in radians.

版本 0.9.4 ( glm::perspective , version 0.9.4 ) 在同一位置注明:

fovy Expressed in radians if GLM_FORCE_RADIANS is define or degrees otherwise.

这是因为一般的 GLM 在不久前从度数更改为弧度。

像这样设置透视投影矩阵:

projection = glm::perspective(
    90.0f * (float)M_PI / 180.0,
    float( WINDOW_WIDTH ) / float( WINDOW_HEIGHT ),
    0.1f, 100.0f );

---

解释:

View 矩阵描述了观察场景的方向和位置。 View 矩阵从世界空间转换到 View (眼睛)空间。

投影矩阵描述了从场景的 3D 点到视口(viewport)的 2D 点的映射。它从眼睛空间转换到剪辑空间，剪辑空间中的坐标通过除以w转换为归一化设备坐标(NDC)。剪辑坐标的组成部分。 NDC 的范围为 (-1,-1,-1) 到 (1,1,1)。
裁剪空间之外的每个几何图形。

在透视投影中，投影矩阵描述了从针孔相机看到的世界中的 3D 点到视口(viewport)的 2D 点的映射。
相机平截头体(截棱锥)中的眼空间坐标映射到立方体(归一化设备坐标)。