Following this tutorial, and making small adjustments for compatibility with OpenGL 3.1, I’ve managed to set up a window with freeGLUT and initialize GLEW, but I cannot draw any shapes. For some reason glUseProgram always returns GL_INVALID_OPERATION, which according to this tutorial means the program is not linked correctly. My source code is almost exactly that which works in the first tutorial, though:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <gl\glew.h>
#include <GL\freeglut.h>
#define WINDOW_TITLE_PREFIX "OpenGL Context"
int numberInput;
int CurrentWidth = 800,
CurrentHeight = 600,
WindowHandle = 0;
unsigned FrameCount = 0;
GLuint
VertexShaderId,
FragmentShaderId,
ProgramId,
VaoId,
VboId,
ColorBufferId;
const GLchar* VertexShader =
{
"#version 130
"\
"layout(location=0) in vec4 in_Position;
"\
"layout(location=1) in vec4 in_Color;
"\
"out vec4 ex_Color;
"\
"void main(void)
"\
"{
"\
" gl_Position = in_Position;
"\
" ex_Color = in_Color;
"\
"}
"
};
const GLchar* FragmentShader =
{
"#version 130
"\
"in vec4 ex_Color;
"\
"out vec4 out_Color;
"\
"void main(void)
"\
"{
"\
" out_Color = ex_Color;
"\
"}
"
};
void Initialize(int, char*[]);
void InitWindow(int, char*[]);
void ResizeFunction(int, int);
void RenderFunction(void);
void TimerFunction(int);
void IdleFunction(void);
void Cleanup(void);
void CreateVBO(void);
void DestroyVBO(void);
void CreateShaders(void);
void DestroyShaders(void);
int main(int argc, char* argv[])
{
Initialize(argc, argv);
glutMainLoop();
//numberInput = getchar();
exit(EXIT_SUCCESS);
}
void Initialize(int argc, char* argv[])
{
GLenum GlewInitResult;
InitWindow(argc, argv);
glewExperimental = GL_TRUE;
GlewInitResult = glewInit();
if (GLEW_OK != GlewInitResult) {
fprintf(
stderr,
"ERROR: %s
",
glewGetErrorString(GlewInitResult)
);
exit(EXIT_FAILURE);
}
fprintf(
stdout,
"INFO: OpenGL Version: %s
",
glGetString(GL_VERSION)
);
CreateShaders();
CreateVBO();
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
}
void InitWindow(int argc, char* argv[])
{
glutInit(&argc, argv);
glutInitContextVersion(3, 1);
glutInitContextFlags(GLUT_FORWARD_COMPATIBLE);
glutInitContextProfile(GLUT_CORE_PROFILE);
glutSetOption(
GLUT_ACTION_ON_WINDOW_CLOSE,
GLUT_ACTION_GLUTMAINLOOP_RETURNS
);
glutInitWindowSize(CurrentWidth, CurrentHeight);
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
WindowHandle = glutCreateWindow(WINDOW_TITLE_PREFIX);
if(WindowHandle < 1) {
fprintf(
stderr,
"ERROR: Could not create a new rendering window.
"
);
exit(EXIT_FAILURE);
}
glutReshapeFunc(ResizeFunction);
glutDisplayFunc(RenderFunction);
glutIdleFunc(IdleFunction);
glutTimerFunc(0, TimerFunction, 0);
glutCloseFunc(Cleanup);
}
void ResizeFunction(int Width, int Height)
{
CurrentWidth = Width;
CurrentHeight = Height;
glViewport(0, 0, CurrentWidth, CurrentHeight);
}
void RenderFunction(void) // Render the scene here
{
++FrameCount;
//CreateShaders();
//CreateVBO();
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0, 3);
glutSwapBuffers();
glutPostRedisplay();
}
void IdleFunction(void)
{
glutPostRedisplay();
}
void TimerFunction(int Value)
{
if (0 != Value) {
char* TempString = (char*)
malloc(512 + strlen(WINDOW_TITLE_PREFIX));
sprintf(
TempString,
"%s: %d Frames Per Second @ %d x %d",
WINDOW_TITLE_PREFIX,
FrameCount * 4,
CurrentWidth,
CurrentHeight
);
glutSetWindowTitle(TempString);
free(TempString);
}
FrameCount = 0;
glutTimerFunc(250, TimerFunction, 1);
}
void Cleanup(void)
{
DestroyShaders();
DestroyVBO();
}
void CreateVBO(void)
{
GLfloat Vertices[] = {
-0.8f, -0.8f, 0.0f, 1.0f,
0.0f, 0.8f, 0.0f, 1.0f,
0.8f, -0.8f, 0.0f, 1.0f
};
GLfloat Colors[] = {
1.0f, 0.0f, 0.0f, 1.0f,
0.0f, 1.0f, 0.0f, 1.0f,
0.0f, 0.0f, 1.0f, 1.0f
};
GLenum ErrorCheckValue = glGetError();
glGenVertexArrays(1, &VaoId);
glBindVertexArray(VaoId);
glGenBuffers(1, &VboId);
glBindBuffer(GL_ARRAY_BUFFER, VboId);
glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(0);
glGenBuffers(1, &ColorBufferId);
glBindBuffer(GL_ARRAY_BUFFER, ColorBufferId);
glBufferData(GL_ARRAY_BUFFER, sizeof(Colors), Colors, GL_STATIC_DRAW);
glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0, 0);
glEnableVertexAttribArray(1);
ErrorCheckValue = glGetError();
if (ErrorCheckValue != GL_NO_ERROR)
{
fprintf(
stderr,
"ERROR: Could not create a VBO: %s
",
gluErrorString(ErrorCheckValue)
);
exit(-1);
}
}
void DestroyVBO(void)
{
GLenum ErrorCheckValue = glGetError();
glDisableVertexAttribArray(1);
glDisableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glDeleteBuffers(1, &ColorBufferId);
glDeleteBuffers(1, &VboId);
glBindVertexArray(0);
glDeleteVertexArrays(1, &VaoId);
ErrorCheckValue = glGetError();
if (ErrorCheckValue != GL_NO_ERROR)
{
fprintf(
stderr,
"ERROR: Could not destroy the VBO: %s
",
gluErrorString(ErrorCheckValue)
);
exit(-1);
}
}
void CreateShaders(void)
{
GLenum ErrorCheckValue = glGetError();
VertexShaderId = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(VertexShaderId, 1, &VertexShader, NULL);
glCompileShader(VertexShaderId);
FragmentShaderId = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(FragmentShaderId, 1, &FragmentShader, NULL);
glCompileShader(FragmentShaderId);
ProgramId = glCreateProgram();
glAttachShader(ProgramId, VertexShaderId);
glAttachShader(ProgramId, FragmentShaderId);
glLinkProgram(ProgramId);
glUseProgram(ProgramId); // This is the problem, but why?
ErrorCheckValue = glGetError();
if (ErrorCheckValue != GL_NO_ERROR)
{
fprintf(
stderr,
"ERROR: Could not create the shaders: %s
",
gluErrorString(ErrorCheckValue)
);
numberInput = getchar();
exit(-1);
}
}
void DestroyShaders(void)
{
GLenum ErrorCheckValue = glGetError();
glUseProgram(0);
glDetachShader(ProgramId, VertexShaderId);
glDetachShader(ProgramId, FragmentShaderId);
glDeleteShader(FragmentShaderId);
glDeleteShader(VertexShaderId);
glDeleteProgram(ProgramId);
ErrorCheckValue = glGetError();
if (ErrorCheckValue != GL_NO_ERROR)
{
fprintf(
stderr,
"ERROR: Could not destroy the shaders: %s
",
gluErrorString(ErrorCheckValue)
);
exit(-1);
}
}
If I comment out glUseProgram, I get the triangle displayed properly, but it’s all white. I don’t understand how the shader program could be failing to link; it’s just a few lines. Can anyone see anything off with my code?
The newer GLSL syntax would’ve been nice, but that’s what I get for having an Intel GPU.