Question

How to draw a triangle using OpenGL with vertex shader and fragment shader in C

Answer 1

#include <GL/glew.h>
#include <GLFW/glfw3.h>

#include <stdio.h>
#include <stdlib.h>

// Draw triangle:
// glCreateShader->glShaderSource->glCreateProgram->glCompileShader
// ->glAttachShader->glLinkProgram->glDetachShader->glDeleteShader
// ->Draw triangle with shader program

static unsigned int CompileShader(unsigned int type, const char* source) {
    unsigned int id = glCreateShader(type);
    glShaderSource(id, 1, &source, NULL);
    glCompileShader(id);

    int ivresult;
    glGetShaderiv(id, GL_COMPILE_STATUS, &ivresult);
    if (ivresult == GL_FALSE) {
        int length;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
        char* errormessage = (char*)malloc(length * sizeof(char));
        glGetShaderInfoLog(id, length, &length, errormessage);
        printf("Failed to compile the %s shader!\n", (type == GL_VERTEX_SHADER ? "vertex" : "fragment"));
        printf("%s\n", errormessage);
        free(errormessage);
        glDeleteShader(id);

        return 0;
    }

    return id;
}

static unsigned int CreateShader(const char* vertexShader, const char* fragmentShader) {
    unsigned int program = glCreateProgram();
    unsigned int vs = CompileShader(GL_VERTEX_SHADER, vertexShader);
    unsigned int fs = CompileShader(GL_FRAGMENT_SHADER, fragmentShader);

    glAttachShader(program, vs);
    glAttachShader(program, fs);
    glLinkProgram(program);
    glValidateProgram(program);

    glDetachShader(program, vs);
    glDetachShader(program, fs);

    glDeleteShader(vs);
    glDeleteShader(fs);

    return program;
}

int main(void)
{
    if (!glfwInit()) {
        printf("glfwInit() Error!");
        return -1;
    }

    GLFWwindow* window = glfwCreateWindow(640, 480, "Window Title", NULL, NULL);
    if (!window) {
        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);

    if (glewInit() != GLEW_OK) {
        printf("glewInit() Error!");
        return -1;
    }

    float positions[6] = {
        -0.4f, -0.4f,
         0.0f,  0.4f,
         0.4f, -0.4f
    };

    unsigned int buffer;
    glGenBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), positions, GL_STATIC_DRAW);

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 2, 0);

    char vertexShader[] =
        "#version 410 core\n"
        "layout(location = 0) in vec4 position;\n"
        "void main() {\n"
        "  gl_Position = position;\n"
        "}\n";

    char fragmentShader[] =
        "#version 410 core\n"
        "layout(location = 0) out vec4 color;\n"
        "void main() {\n"
        "  color = vec4(1.0, 1.0, 0.0, 1.0);\n"
        "}\n";

    unsigned int shader = CreateShader(vertexShader, fragmentShader);
    glUseProgram(shader);

    glClearColor(0.752941f, 0.752941f, 0.752941f, 1.0f);

    while (!glfwWindowShouldClose(window)) {
        glClear(GL_COLOR_BUFFER_BIT);

        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);

        glfwPollEvents();
    }

    glDeleteProgram(shader);

    glfwTerminate();

    return 0;
}



/*
run:


*/

 

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