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How to draw 2 triangles in two colors with two shader programs and two different fragment shader in OpenGL with C++

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77 views
asked Jul 31, 2021 by avibootz
edited Aug 1, 2021 by avibootz

1 Answer

0 votes
#include <glad/glad.h>
#include <glfw3.h>

#include <iostream>

const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

const char* vertexShaderSource =
"#version 450 core\n"
"layout (location = 0) in vec3 aPos;\n"
"void main()\n"
"{\n"
"   gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);\n"
"}\n\0";

const char* fragmentShaderBlueSource =
"#version 450 core\n"
"out vec4 FragmentColor;\n"
"void main()\n"
"{\n"
"   FragmentColor = vec4(0.0f, 0.0f, 1.0f, 1.0f);\n"
"}\n\0";

const char* fragmentShaderYellowSource =
"#version 450 core\n"
"out vec4 FragmentColor;\n"
"void main()\n"
"{\n"
"   FragmentColor = vec4(1.0f, 1.0f, 0.0f, 0.0f);\n"
"}\n\0";

// glfw: when window size changed this callback function executes // glfwSetFramebufferSizeCallback
void framebuffer_size_callback(GLFWwindow* window, int width, int height) {
    // glfw: the viewport matches the new window dimensions
    glViewport(0, 0, width, height);
}

// glfw: process keys
void processInput(GLFWwindow* window) {
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

int main()
{
    // glfw: initialize
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 5);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    // glfw: create window
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "Window Title", NULL, NULL);
    if (window == NULL) {
        std::cout << "Failed to create GLFW window" << "\n";
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    // glad: load all OpenGL function pointers
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
        std::cout << "Failed to initialize GLAD" << "\n";
        return -1;
    }

    // build and compile shader program
    int success;
    char errorInfo[512] = "";

    // vertex shader
    unsigned int vertexShader = glCreateShader(GL_VERTEX_SHADER);

    unsigned int fragmentShaderBlue = glCreateShader(GL_FRAGMENT_SHADER);
    unsigned int fragmentShaderYellow = glCreateShader(GL_FRAGMENT_SHADER);

    unsigned int shaderProgramBlue = glCreateProgram();
    unsigned int shaderProgramYellow = glCreateProgram(); 

    glShaderSource(vertexShader, 1, &vertexShaderSource, NULL);
    glCompileShader(vertexShader);

    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(vertexShader, 512, NULL, errorInfo);
        std::cout << "glCompileShader(vertexShader); FAILED\n" << errorInfo << "\n";
    }

    glShaderSource(fragmentShaderBlue, 1, &fragmentShaderBlueSource, NULL);
    glCompileShader(fragmentShaderBlue);

    glGetShaderiv(fragmentShaderBlue, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(fragmentShaderBlue, 512, NULL, errorInfo);
        std::cout << "glCompileShader(fragmentShaderBlue); FAILED\n" << errorInfo << "\n";
    }

    glShaderSource(fragmentShaderYellow, 1, &fragmentShaderYellowSource, NULL);
    glCompileShader(fragmentShaderYellow);

    glGetShaderiv(fragmentShaderYellow, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(fragmentShaderYellow, 512, NULL, errorInfo);
        std::cout << "glCompileShader(fragmentShaderYellow); FAILED\n" << errorInfo << "\n";
    }

    glAttachShader(shaderProgramBlue, vertexShader);
    glAttachShader(shaderProgramBlue, fragmentShaderBlue);
    glLinkProgram(shaderProgramBlue);

    glAttachShader(shaderProgramYellow, vertexShader);
    glAttachShader(shaderProgramYellow, fragmentShaderYellow);
    glLinkProgram(shaderProgramYellow);

    // delete shaders after linking
    glDeleteShader(vertexShader);
    glDeleteShader(shaderProgramBlue);
    glDeleteShader(shaderProgramYellow);

    // set vertex data 
    float firstTriangleVertices[] = {
        -0.9f, -0.6f, 0.0f, // left (x=-1,y=0 : x=0,y=-1)
        -0.0f, -0.6f, 0.0f, // right (x=0,y=-1 : x=1,y=0)
        -0.45f, 0.6f, 0.0f  // top (x=0,y=1)
    };
    float secondTriangleVertices[] = {
        0.0f, -0.6f, 0.0f,  // left
        0.9f, -0.6f, 0.0f,  // right
        0.45f, 0.6f, 0.0f   // top 
    };

    // set buffers vertex buffer object anb vertex array object
    unsigned int VBO[2], VAO[2];
    glGenVertexArrays(2, VAO);
    glGenBuffers(2, VBO);

    // first triangle
    glBindVertexArray(VAO[0]);
    glBindBuffer(GL_ARRAY_BUFFER, VBO[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(firstTriangleVertices), firstTriangleVertices, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);

    // second triangle setup
    glBindVertexArray(VAO[1]);	
    glBindBuffer(GL_ARRAY_BUFFER, VBO[1]);	
    glBufferData(GL_ARRAY_BUFFER, sizeof(secondTriangleVertices), secondTriangleVertices, GL_STATIC_DRAW);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
    glEnableVertexAttribArray(0);

    // render loop
    while (!glfwWindowShouldClose(window)) {
        processInput(window);

        // render
        glClearColor(0.2f, 0.3f, 0.4f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        glUseProgram(shaderProgramBlue);
        // draw first triangle
        glBindVertexArray(VAO[0]);
        glDrawArrays(GL_TRIANGLES, 0, 3);

        glUseProgram(shaderProgramYellow);
        // draw the second triangle
        glBindVertexArray(VAO[1]);
        glDrawArrays(GL_TRIANGLES, 0, 3);

        // glfw: swap buffers
        glfwSwapBuffers(window);

        // glfw: poll IO events (keys & mouse)
        glfwPollEvents();

    }

    // de-allocate all resources
    glDeleteVertexArrays(2, VAO);
    glDeleteBuffers(2, VBO);
    glDeleteProgram(shaderProgramBlue);
    glDeleteProgram(shaderProgramYellow);

    // glfw: terminate and clear all previously GLFW allocated resources
    glfwTerminate();

    return 0;
}

 





answered Jul 31, 2021 by avibootz
edited Jul 31, 2021 by avibootz
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