Question

我正在尝试提供http://www.opengl-tutorial.org/beginners-tutorials/tutorial-3-matrices/

的教程

这里是完整的代码：

//============================================================================
// Name        : TestOpenGLGLFW.cpp
// Author      : Manohar Kuse
// Version     :
// Copyright   : GNU Licence
// Description : http://www.opengl-tutorial.org/beginners-tutorials/tutorial-1-opening-a-window/
//============================================================================

#include <iostream>

#include <GL/glew.h>

#include <GLFW/glfw3.h>

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtx/transform.hpp>


#include "LoadShader.h"


int main( int argc, char ** argv )
{
    // --1-- Initialise GLFW
    if( glfwInit() == false )
    {
        std::cerr << "Failed to initialize GLFW3\nQuiting....\n";
        exit(1);
    }


    // --2-- Create Window
    glfwWindowHint(GLFW_SAMPLES, 4); // 4x antialiasing
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); // We want OpenGL 3.3
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); //We don't want the old OpenGL

    GLFWwindow * window=NULL;
    window = glfwCreateWindow( 400, 400, "hello", NULL, NULL );
    if( window == NULL )
    {
        std::cerr << "Failed to create glfw window\nQuiting....\n";
        glfwTerminate();
        exit(1);
    }

    // --3-- Make current context
    glfwMakeContextCurrent( window );



    // --4-- GLEW (Wrangler lib)
    glewExperimental=true; // Needed in core profile
    if (glewInit() != GLEW_OK)
    {
        std::cerr << "Failed to initialize GLEW\n";
        glfwTerminate();
        exit(1);
    }


            // --4.1-- Create a VAO
            GLuint vertexArrayId;
            glGenVertexArrays( 1, &vertexArrayId ); // generate just 1 vertex array
            glBindVertexArray( vertexArrayId );

            // --4.2-- Define a float array, denoting 3 cords of a triangle
             GLfloat vertexData[] = {
                    -1.0, -1.0,  0.0,
                     1.0, -1.0,  0.0,
                     0.0,  1.0,  0.0
            };

            // --4.3-- Create a VBO (vertex buffer)
            GLuint vertexBufferId;
            glGenBuffers( 1, &vertexBufferId );
            glBindBuffer( GL_ARRAY_BUFFER, vertexBufferId );

            //give our vertices to OpenGL
            glBufferData( GL_ARRAY_BUFFER, sizeof( vertexData), vertexData, GL_STATIC_DRAW );

            // --4.4-- Load vertex & fragment shaders
            GLuint programID = LoadShaders( "src/shaders/vertex.shader", "src/shaders/fragment.shader" );


    // --5-- Main loop
    glfwSetInputMode( window, GLFW_STICKY_KEYS, GL_TRUE );
    glClearColor(0,0,.4,0);


    glm::mat4 Projection = glm::perspective(45.0f, 4.0f/3.0f, .1f, 100.0f );
    //glm::mat4 Projection = glm::ortho(-2.0f, 2.0f, -2.0f, 2.0f );

    glm::mat4 View = glm::lookAt( glm::vec3(4,3,3), glm::vec3(0,0,0), glm::vec3(0,1,0) );

    glm::mat4 Model = glm::mat4( 1.0 );

    glm::mat4 MVP = Projection * View * Model;

    GLuint matrixId = glGetUniformLocation( programID, "MVP" );

    glUniformMatrix4fv(matrixId, 1, GL_FALSE, &MVP[0][0]);


    do
    {
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        glUseProgram( programID );
        // draw
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(
           0,                  // attribute 0. No particular reason for 0, but must match the layout in the shader.
           3,                  // size
           GL_FLOAT,           // type
           GL_FALSE,           // normalized?
           0,                  // stride
           (void*)0            // array buffer offset
        );

        glDrawArrays(GL_TRIANGLES, 0, 3); // Starting from vertex 0; 3 vertices total -> 1 triangle

        glDisableVertexAttribArray(0);

        // swap buffers
        glfwSwapBuffers( window );
        glfwPollEvents();
    }
    while( glfwWindowShouldClose(window)==false );



}

顶点着色器：

#version 330 core

layout(location = 0) in vec3 vertexPosition_modelspace;
uniform mat4 MVP ;

void main(){
    vec4 v = vec4(vertexPosition_modelspace,1); // Transform an homogeneous 4D vector, remember ?
    gl_Position =  MVP *v;
 }

Fragment Shader：

#version 330 core
out vec3 color;

void main(){
    color = vec3(1,0,0);
}

我看不到我的三角形是画画，而是看到背景颜色。但是，如果我删除转换代码（Model＆lt; View，Projection），我会看到三角形。可能是什么问题？

Answer 1

glUniform*()函数为当前绑定程序设置制服。因此，您需要在glUseProgram()来电之前移动glUniformMatrix4fv()来电：

glUseProgram(programID);
glUniformMatrix4fv(matrixId, 1, GL_FALSE, &MVP[0][0]);

每当某些内容在您的OpenGL代码中无法正常工作时，您应该调用glGetError()，并查看它是否报告任何错误。在这种情况下，您将从glUniformMatrix4fv()收到错误。来自man page的错误列表：

如果没有当前的程序对象，则生成GL_INVALID_OPERATION。

OpenGL 4.1引入了一组入口点，用于设置统一值而不绑定程序。在这种情况下，将应用以下调用：

glProgramUniformMatrix4fv(programID, matrixId, 1, GL_FALSE, &MVP[0][0]);

OpenGL3.3无法看到模型

1 个答案: