即使没有发生错误，openGL屏幕上也不会绘制三角形

Question

I have written a simple openGL program to draw a triangle on the screen. I have done debugging with glGetError() and now there is no error in the code but when I try to run it only a black screen comes up.

here is my code. I am using GLFW for window creation.

#include<glew.h>
#include<glfw3.h>
#include<stdio.h>

int main(int argc, char ** argv)
{
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);

    GLFWwindow* window = glfwCreateWindow(800, 600, "OpenGL", nullptr,           nullptr);
    glfwMakeContextCurrent(window);

    glewExperimental = GL_TRUE;
    glewInit();

    float vertices[] = {
        0.0f, 0.5f,
        0.5f, -0.5f,
       -0.5f, -0.5f
    };
    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    const  GLchar * vs =
        "#version 150\n"
        "in vec2 position;\n"
        "void main() {\n"
        "vec4 gl_Position = vec4( position , 0.0 , 1.0 );\n"
        "}";

    const GLchar * fs =
         "#version 150\n"
         "out vec4 out_color; \n"
         "void main() { \n"
         "out_color = vec4(1.0, 1.0, 1.0, 1.0);\n"
         "}";

    GLuint vsh = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vsh, 1, &vs, NULL);
    glCompileShader(vsh);
    GLint status;
    glGetShaderiv(vsh, GL_COMPILE_STATUS, &status);
    if (status == GL_TRUE) printf("Vertex Shader Compiled success\n");

    GLuint fsh = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fsh, 1, &fs, NULL);
    glCompileShader(fsh);
    glGetShaderiv(fsh, GL_COMPILE_STATUS, &status);
    if (status == GL_TRUE) printf("Fragment Shader Compiled success\n");

    GLuint sp = glCreateProgram();
    glAttachShader(sp, vsh);
    glAttachShader(sp, fsh);
    glBindFragDataLocation(sp, 0, "out_color");
    glBindAttribLocation(sp,1,"position");
    glLinkProgram(sp);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, 0);
    glEnableVertexAttribArray(1);

    glUseProgram(sp);

    while (!glfwWindowShouldClose(window))
    {
        glClear(GL_COLOR_BUFFER_BIT);
        glDrawArrays(GL_TRIANGLES, 0, 3);
        glfwSwapBuffers(window);
        glfwPollEvents();
    }
    glfwTerminate();
    return 0;    
} 

Update I have narrowed down the issue to just one line of code

 GLint pos = glGetAttribLocation(sp, "position") //sp is shader program

The problem is it is returning -1. I have read in tutorials that if you don't use a variable it will be optimized out by the compiler.I have used the position in the code then why it is getting thrown away. Below is my vertex shader.

const  GLchar * vs =
        "#version 150\n"
        "in vec2 position;\n"
        "void main() {\n"
        "vec4 gl_Position = vec4( position , 0.0 , 1.0 );\n"
        "}";

Answer 1

just add these lines after glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

glEnableVertexAttribArray(0); glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, 0);

I mean use location 0 instead of 1 hope this helps