C++ OpenGL渲染两个不同颜色的矩形

Posted 2023-02-22

【中文标题】C++ OpenGL渲染两个不同颜色的矩形

【英文标题】：C++ OpenGL rendering two rectangles with different colors

【发布时间】：2016-07-06 22:07:28

【问题描述】：

我试图创建两个具有两种不同颜色并朝相反方向移动的矩形对象。但是，我被困在用不同颜色渲染两个矩形（目前它们是相同的颜色）。

有什么办法呢？

代码如下：

#include <stdio.h>
#include <string.h>

#include <math.h>
#include <GL/glew.h>
#include <GL/freeglut.h>

#include "ogldev_util.h"
#include "ogldev_math_3d.h"

GLuint VBO1;
GLuint VBO2;
GLuint gScaleLocation1;
GLuint gScaleLocation2;

const char* pVSFileName = "shader.vs";
const char* pFSFileName = "shader.fs";


static void RenderSceneCB()

    glClear(GL_COLOR_BUFFER_BIT);


    static float Scale1 = 0.0f;

    Scale1 += 0.01f;

    glUniform1f(gScaleLocation1, sinf(Scale1));

    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, VBO1);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
    glDrawArrays(GL_TRIANGLES, 0, 6);

    static float Scale2 = 0.0f;

    Scale2 -= 0.01f;

    glUniform1f(gScaleLocation2, sinf(Scale2));

    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, VBO2);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
    glDrawArrays(GL_TRIANGLES, 0, 6);

    glDisableVertexAttribArray(0);

    glutSwapBuffers();



static void InitializeGlutCallbacks()

    glutDisplayFunc(RenderSceneCB);
    glutIdleFunc(RenderSceneCB);


static void CreateVertexBuffer()

    Vector3f Vertices[6];
    Vertices[0] = Vector3f(1.0f, -0.5f, 0.0f);
    Vertices[1] = Vector3f(1.0f, 0.5f, 0.0f);
    Vertices[2] = Vector3f(3.0f, -0.5f, 0.0f);

    Vertices[3] = Vector3f(1.0f, 0.5f, 0.0f);
    Vertices[4] = Vector3f(3.0f, 0.5f, 0.0f);
    Vertices[5] = Vector3f(3.0f, -0.5f, 0.0f);

    glGenBuffers(1, &VBO1);
    glBindBuffer(GL_ARRAY_BUFFER, VBO1);
    glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW);

    Vector3f Vertices2[6];
    Vertices2[0] = Vector3f(-3.0f, -0.5f, 0.0f);
    Vertices2[1] = Vector3f(-3.0f, 0.5f, 0.0f);
    Vertices2[2] = Vector3f(-1.0f, -0.5f, 0.0f);

    Vertices2[3] = Vector3f(-3.0f, 0.5f, 0.0f);
    Vertices2[4] = Vector3f(-1.0f, 0.5f, 0.0f);
    Vertices2[5] = Vector3f(-1.0f, -0.5f, 0.0f);

    glGenBuffers(1, &VBO2);
    glBindBuffer(GL_ARRAY_BUFFER, VBO2);
    glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices2), Vertices2, GL_STATIC_DRAW);


static void AddShader(GLuint ShaderProgram, const char* pShaderText, GLenum ShaderType)

    GLuint ShaderObj = glCreateShader(ShaderType);

    if (ShaderObj == 0) 
        fprintf(stderr, "Error creating shader type %d\n", ShaderType);
        exit(1);
    

    const GLchar* p[1];
    p[0] = pShaderText;
    GLint Lengths[1];
    Lengths[0]= strlen(pShaderText);
    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 type %d: '%s'\n", ShaderType, InfoLog);
        exit(1);
    

    glAttachShader(ShaderProgram, ShaderObj);


static void CompileShaders()

    GLuint ShaderProgram = glCreateProgram();

    if (ShaderProgram == 0) 
        fprintf(stderr, "Error creating shader program\n");
        exit(1);
    

    string vs, fs;

    if (!ReadFile(pVSFileName, vs)) 
        exit(1);
    ;

    if (!ReadFile(pFSFileName, fs)) 
        exit(1);
    ;

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

    GLint Success = 0;
    GLchar ErrorLog[1024] =  0 ;

    glLinkProgram(ShaderProgram);
    glGetProgramiv(ShaderProgram, GL_LINK_STATUS, &Success);
    if (Success == 0) 
        glGetProgramInfoLog(ShaderProgram, sizeof(ErrorLog), NULL, ErrorLog);
        fprintf(stderr, "Error linking shader program: '%s'\n", ErrorLog);
        exit(1);
    

    glValidateProgram(ShaderProgram);
    glGetProgramiv(ShaderProgram, GL_VALIDATE_STATUS, &Success);
    if (!Success) 
        glGetProgramInfoLog(ShaderProgram, sizeof(ErrorLog), NULL, ErrorLog);
        fprintf(stderr, "Invalid shader program: '%s'\n", ErrorLog);
        exit(1);
    

    glUseProgram(ShaderProgram);

    gScaleLocation1 = glGetUniformLocation(ShaderProgram, "gScale");
    assert(gScaleLocation1 != 0xFFFFFFFF);



int main(int argc, char** argv)

    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGBA);
    glutInitWindowSize(1024, 768);
    glutInitWindowPosition(100, 100);
    glutCreateWindow("Tutorial 05");

    InitializeGlutCallbacks();

    // Must be done after glut is initialized!
    GLenum res = glewInit();
    if (res != GLEW_OK) 
      fprintf(stderr, "Error: '%s'\n", glewGetErrorString(res));
      return 1;
    

    printf("GL version: %s\n", glGetString(GL_VERSION));

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

    CreateVertexBuffer();

    CompileShaders();

    glutMainLoop();

    return 0;

片段着色器

#version 330

out vec4 FragColor;

void main()

    FragColor = vec4(1.0, 0.0, 0.0, 1.0);

【问题讨论】：

我们看不到您的着色器，但我看不到您设置任何颜色统一或顶点数组绑定。您需要将带有顶点的颜色作为不同的顶点数组绑定、统一变量或纹理推送。您也不需要在每次渲染时都设置顶点属性指针。您可能应该改用适当的 VAO，因此您可以交换您的 VAO 绑定来渲染多个网格。

【参考方案1】：

这取决于。在这种情况下，最简单的方法是在片段着色器中添加uniform vec3 color; 和gl_FragColor = vec4(color, 1.0);，然后在渲染每个矩形之前通过调用glUniform3f 将其初始化为所需的颜色。但是，随着矩形计数的增长，您最好创建顶点struct，它不仅会携带坐标，还会携带颜色。 另外，我强烈推荐这个http://www.opengl-tutorial.org/ opengl 教程网站。

【讨论】：

我已经在片段着色器中添加了颜色，但是我如何将它调用为一绿一红？ glUniform3f 的正确使用方法是什么？

您需要在glUseProgram 和glDrawArrays 之间的任意位置调用它。第一个参数是一个统一的位置，接下来是 3 - 矢量的每个分量（在这种情况下，颜色 - rgb。它们应该在 0.0 和 1.0 之间）：glUniform3f(colorUniformLocation, r, g, b);。在您的情况下，它是：glUniform1f(gScaleLocation1, sinf(Scale1)); 之后的glUniform3f(colorUniformLocation, 1.0f, 0.0f, 0.0f); 和glUniform1f(gScaleLocation1, sinf(Scale2)); 之后的glUniform3f(colorUniformLocation, 0.0f, 1.0f, 0.0f);。