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I am new to OpenGL and i want to draw a simple triangle on screen with my shader. I set up buffers and wrote a shaders but it doesn't seem to work. It gives white screen, i tried to change glCreateBuffer with glGenBuffer and screen turned to black screen. I want to create&compile shaders in one function called createAndCompileShader(...), buffers are defined in main function.

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

static unsigned int createAndCompileShader(const char* vertexShader, const char* fragmentShader) {

    unsigned int fragmentShaderr = glCreateShader(GL_FRAGMENT_SHADER);
    unsigned int vertexShaderr = glCreateShader(GL_VERTEX_SHADER);

    glShaderSource(vertexShaderr, 1, &vertexShader, NULL);
    glShaderSource(fragmentShaderr, 1, &fragmentShader, NULL);

    glCompileShader(vertexShaderr);
    glCompileShader(fragmentShaderr);

    unsigned int program = glCreateProgram();

    glAttachShader(program, vertexShaderr);
    glAttachShader(program, fragmentShaderr);
    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);

    float vertexPositions[6] = {
             -0.5, -0.5,
             0.0, 0.5,
             0.5, -0.5
    };


    const char* vertexShader = "#version 330 core\n"
        "layout(location = 0) in vec4 position;\n"
        "void main()\n"
        "{\n"
        "gl_Position = position;\n"
        "}\n";

    const char* fragementShader = "#version 330 core\n"
        "layout(location = 0) in vec4 position;\n"
        "void main()\n"
        "{\n"
        "color = vec4(1.0, 0.0, 0.0, 1.0);\n"
        "}\n";

    unsigned int program = createAndCompileShader(vertexShader, fragementShader);

    glUseProgram(program);

    unsigned int buffer;

    glGenBuffers(1, &buffer);
    //glCreateBuffers(1, &buffer);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, 6 * sizeof(float), vertexPositions, GL_STATIC_DRAW);

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

  
    //std::string vertexShader;
    //std::string fragmentShader;

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


        glDrawArrays(GL_TRIANGLES, 0 ,3);

        /*glBegin(GL_TRIANGLES);
        glVertex2f(-0.5, -0.5);
        glVertex2f( 0.0, 0.5);
        glVertex2f( 0.5, -0.5);
        glEnd();*/

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

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

    glDeleteProgram(program);

    glfwTerminate();
    return 0;
}
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  • Do some error handling in your createAndCompileShader Commented Oct 24, 2020 at 14:29
  • I tried that, but i didn't see any error about syntax etc. Commented Oct 24, 2020 at 14:46

1 Answer 1

Reset to default
3

Fragment shader input layout locations qualifiers are not provided in GLSL 3.30. You have to switch to GLSL 4.10 or remove the layout location in the fragment shader:

layout(location = 0) in vec4 position;

in vec4 position;

Furthermore you missed the specification of the fragment shader output color.

#version 330 core
in vec4 position;
out vec4 color;
void main()
{
    color = vec4(1.0, 0.0, 0.0, 1.0);
}

I recommend to use Raw string liters:

const char* fragementShader = R"(#version 330 core
in vec4 position;
out vec4 color;
void main()
{
    color = vec4(1.0, 0.0, 0.0, 1.0);
})";

Check if the shader compilation succeeded and if the program object linked successfully.
If the compiling of a shader succeeded can be checked by glGetShaderiv and the parameter GL_COMPILE_STATUS.
If the linking of a program was successful can be checked by glGetProgramiv and the parameter GL_LINK_STATUS.
(See the answer to this question.)

If you use a core profile OpenGL Context, the the default Vertex Array Object is not valid. Create a named VAO:

unsigned int VAO;
glCreateVertexArrays(1, &VAO);
glBindVertexArray(VAO);

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

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

GLEW has to be initialized by glewInit(). See Initializing GLEW:

glfwMakeContextCurrent(window);
glewInit();
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5 Comments

@Bcrx It works fine for me. Just copy the shader code.
It worked!, little inattention, i'll be more careful after this, thank you for your help.
@Rabbid76 I have frequently used layout location qualifiers for vertex shaders, glsl 3.30, without any problems. Only in Visual Studio using an extension for glsl support was I presented with warning, but I just ignored it and it still worked fine. You wouldn't happen to know why that could be?
@ワイきんぐ Please read the answer: Fragment shader input layout locations qualifiers [...]. Of course vertex shader input layout qualifiers are valid in GLSL 3.30
That's weird, because I always got this warning for vertex shaders. But thanks!

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