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Thread: Suspected fragment shader problem, No color, OpenGL 4, GLFW 3, GLEW

  1. #1
    Junior Member Newbie
    Join Date
    Jun 2012

    Suspected fragment shader problem, No color, OpenGL 4, GLFW 3, GLEW

    I am using OpenGL 4.1, GLFW 3 and GLEW. I am trying to draw a simple triangle with the color purple.

    The triangle is drawn, the color is not.

    This code is from a tutorial, I had to update the GLFW calls to reflect GLFW 3.x. As far as I can tell, the color shader appears to be correct.

    EDIT: Solved a problem where the GLFW window is unresponsive to key presses and mouse clicks. Need to include call to glfwPollEvents() within the drawing loop. Still no color.

    Code :
    #include <GL/glew.h> // include GLEW and new version of GL on Windows
    #include <GL/glfw3.h> // GLFW helper library
    #include <stdio.h>
    #include <string>
    #include <iostream>
    int main () {
    	GLFWwindow* window;
      // start GL context and O/S window using the GLFW helper library
      if(!glfwInit ()){
    	  std::cout << "Failed at glfwInit()!" << std::endl;
    	  return -1;
      // "hint" that the version 4.2 should be run with no back-compat stuff
      int major = 4;
    	int minor = 1;
    	glfwWindowHint (GLFW_CONTEXT_VERSION_MAJOR, major);
    	glfwWindowHint (GLFW_CONTEXT_VERSION_MINOR, minor);
      // open a window of sixe 640x480 
      window = glfwCreateWindow(640, 480, "Window!!!", NULL, NULL);
    	  std::cout << "Failed at window creation!" << std::endl;
    	  return -1;
      // start GLEW extension handler
      GLenum err = glewInit ();
      if(GLEW_OK != err){
    	  std::cout << "glewInit failed!!!" << std::endl;
    	  return -1;
      // get version info
      const GLubyte* renderer = glGetString (GL_RENDERER); // get renderer string
      const GLubyte* version = glGetString (GL_VERSION); // version as a string
      printf("Renderer: %s\n", renderer);
      printf("OpenGL version supported %s\n", version);
    	// tell GL to only draw onto a pixel if the shape is closer to the viewer
      glEnable (GL_DEPTH_TEST); // enable depth-testing
      glDepthFunc (GL_LESS); // depth-testing interprets a smaller value as "closer"
      int i;
      //A triangle's vertices
      float points[] = {
    	  0.0f, 0.5f, 0.0f,
    	  0.5f, -0.5f, 0.0f,
    	  -0.5f, -0.5f, 0.0f
      //Create and setup vertex buffer object
      unsigned int vbo = 0;
      glGenBuffers(1, &vbo);
      glBindBuffer(GL_ARRAY_BUFFER, vbo);
      glBufferData(GL_ARRAY_BUFFER, 9 * sizeof(float), &points[0], GL_STATIC_DRAW);
      //Create and setup vertex array (or attribute?) object to store vbo point data
      unsigned int vao = 0;
      glGenVertexArrays(1, &vao);
      glBindBuffer(GL_ARRAY_BUFFER, vbo);
      glVertexAttribPointer(0,3, GL_FLOAT, GL_FALSE, 0, (GLubyte*)NULL);
      std::string vertex_shader = 
    	  "in vec3 vp;"
    	  "void main () {"
    	  "	gl_Position = vec4(vp, 1.0);"
      std::string fragment_shader = 
    	  "out vec4 frag_color;"
    	  "void main() {"
    	  "	frag_color = vec4 (0.5, 0.0, 0.5, 1.0f);"
      unsigned int vs = glCreateShader(GL_VERTEX_SHADER);
      const char* str = vertex_shader.c_str();
      glShaderSource(vs, 1, &str, NULL);
      unsigned int fs = glCreateShader (GL_FRAGMENT_SHADER);
      const char* strb = fragment_shader.c_str();
      glShaderSource (fs, 1, &strb, NULL);
      unsigned int shader_program = glCreateProgram();
      glAttachShader(shader_program, fs);
      glAttachShader(shader_program, vs);
      bool running = true;
      while (running){
    	  glDrawArrays(GL_TRIANGLES, 0, 3);
    	  running = !glfwGetKey(window, GLFW_KEY_ESCAPE) && !glfwWindowShouldClose(window);
    	  glfwPollEvents(); //Needs to be called or else window is completely unresponsive to move, resize, close, key strokes, etc
      // close GL context and any other GLFW resources
      return 0;
    Last edited by WaywardSquanderer; 07-21-2013 at 07:43 PM.

  2. #2
    Junior Member Newbie
    Join Date
    Jun 2012
    Forgot to include version number and layout statement in shader files/strings! So does this mean the tutorial is wrong or do some shaders compile fine with

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