Fragment shader did not work

OpenGL
1

Hi,
I am trying to draw one triangle with inline shader program. Red value was specified in fragment shader, but write appeared instead.

Here are the file contents:

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

static unsigned int compileShader(unsigned int type, const std::string& source) {
    unsigned int id = glCreateShader(type);
    const char* src = source.c_str();
    glShaderSource(id, 1, &src, nullptr);
    glCompileShader(id);

    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);
    if (result == GL_FALSE) {
        int length;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length);
        char* message = (char*)alloca(length * sizeof(char));
        glGetShaderInfoLog(id, length, &length, message);
        std::cout << "Failed to compile " << 
            ( (type == GL_VERTEX_SHADER) ?  "vertex shader" : "fragment shader" ) 
            << std::endl;
    }


    return 0;
}

static int createShader(const std::string& vertexShader, const std::string& 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);

    return program;
}

int main(void)
{
    GLFWwindow* window;

    /* Initialize the library */
    if (!glfwInit())
        return -1;

    /* Create a windowed mode window and its OpenGL context */
    window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    /* Make the window's context current */
    glfwMakeContextCurrent(window);

    GLenum err = glewInit();
    if (err != GLEW_OK) {
        std::cout << "glewInit Error" << std::endl;
    }

    std::cout << glGetString(GL_VERSION) << std::endl;

    float positions[6] = {
        -.5f, -.5f,
        -.5f, .0f,
        .0f, .5f
    };

    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, 
        2 * sizeof(float), 
        0);

    std::string vertexShader =
        "#version 330 core\n\n"
        "layout(location = 0) in vec4 position;\n\n"
        "void main()\n"
        "{\n"
        "   gl_Position = position;\n"
        "}\n";

    std::string fragmentShader =
        "#version 330 core\n\n"
        "layout(location = 0) out vec4 color;\n\n"
        "void main()\n"
        "{\n"
        "   color = vec4(1.0, 0.0, 0.0, 1.0)\n"
        "}\n";

    unsigned int shader = createShader(vertexShader, fragmentShader);
    glUseProgram(shader);
        
    //glBindBuffer(GL_ARRAY_BUFFER, 0);


    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window))
    {
        /* Render here */
        glClear(GL_COLOR_BUFFER_BIT);

        //glBegin(GL_TRIANGLES);
        //glVertex2f(-.5f, -.5f);
        //glVertex2f(-.5f, .0f);
        //glVertex2f(.0f, .5f);
        //glEnd();

        glDrawArrays(GL_TRIANGLES, 0, 3);

        /* Swap front and back buffers */
        glfwSwapBuffers(window);

        /* Poll for and process events */
        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}

Any Help will be much appreciated.

Kind Regards
KKK

2

compileShader should return the shader name (handle, ID), not zero. Also, the line:

is missing the terminating semicolon.

1 Like
3

It works. Thank you for your help !