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koute/opengl3_hello.c

Created November 9, 2013 23:16
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Minimal SDL2 + OpenGL3 example.
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opengl3_hello.c
/*
Minimal SDL2 + OpenGL3 example.
Author: https://github.com/koute
This file is in the public domain; you can do whatever you want with it.
In case the concept of public domain doesn't exist in your jurisdiction
you can also use this code under the terms of Creative Commons CC0 license,
either version 1.0 or (at your option) any later version; for details see:
http://creativecommons.org/publicdomain/zero/1.0/
This software is distributed without any warranty whatsoever.
Compile and run with: gcc opengl3_hello.c `sdl2-config --libs --cflags` -lGL -Wall && ./a.out
*/
#define GL_GLEXT_PROTOTYPES
#include <SDL.h>
#include <SDL_opengl.h>
#include <stdio.h>
typedef float t_mat4x4[16];
static inline void mat4x4_ortho( t_mat4x4 out, float left, float right, float bottom, float top, float znear, float zfar )
{
#define T(a, b) (a * 4 + b)
out[T(0,0)] = 2.0f / (right - left);
out[T(0,1)] = 0.0f;
out[T(0,2)] = 0.0f;
out[T(0,3)] = 0.0f;
out[T(1,1)] = 2.0f / (top - bottom);
out[T(1,0)] = 0.0f;
out[T(1,2)] = 0.0f;
out[T(1,3)] = 0.0f;
out[T(2,2)] = -2.0f / (zfar - znear);
out[T(2,0)] = 0.0f;
out[T(2,1)] = 0.0f;
out[T(2,3)] = 0.0f;
out[T(3,0)] = -(right + left) / (right - left);
out[T(3,1)] = -(top + bottom) / (top - bottom);
out[T(3,2)] = -(zfar + znear) / (zfar - znear);
out[T(3,3)] = 1.0f;
#undef T
}
static const char * vertex_shader =
"#version 130\n"
"in vec2 i_position;\n"
"in vec4 i_color;\n"
"out vec4 v_color;\n"
"uniform mat4 u_projection_matrix;\n"
"void main() {\n"
" v_color = i_color;\n"
" gl_Position = u_projection_matrix * vec4( i_position, 0.0, 1.0 );\n"
"}\n";
static const char * fragment_shader =
"#version 130\n"
"in vec4 v_color;\n"
"out vec4 o_color;\n"
"void main() {\n"
" o_color = v_color;\n"
"}\n";
typedef enum t_attrib_id
{
attrib_position,
attrib_color
} t_attrib_id;
int main( int argc, char * argv[] )
{
SDL_Init( SDL_INIT_VIDEO );
SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
SDL_GL_SetAttribute( SDL_GL_ACCELERATED_VISUAL, 1 );
SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 8 );
SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 8 );
SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 8 );
SDL_GL_SetAttribute( SDL_GL_ALPHA_SIZE, 8 );
SDL_GL_SetAttribute( SDL_GL_CONTEXT_MAJOR_VERSION, 3 );
SDL_GL_SetAttribute( SDL_GL_CONTEXT_MINOR_VERSION, 2 );
SDL_GL_SetAttribute( SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE );
static const int width = 800;
static const int height = 600;
SDL_Window * window = SDL_CreateWindow( "", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, width, height, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN );
SDL_GLContext context = SDL_GL_CreateContext( window );
GLuint vs, fs, program;
vs = glCreateShader( GL_VERTEX_SHADER );
fs = glCreateShader( GL_FRAGMENT_SHADER );
int length = strlen( vertex_shader );
glShaderSource( vs, 1, ( const GLchar ** )&vertex_shader, &length );
glCompileShader( vs );
GLint status;
glGetShaderiv( vs, GL_COMPILE_STATUS, &status );
if( status == GL_FALSE )
{
fprintf( stderr, "vertex shader compilation failed\n" );
return 1;
}
length = strlen( fragment_shader );
glShaderSource( fs, 1, ( const GLchar ** )&fragment_shader, &length );
glCompileShader( fs );
glGetShaderiv( fs, GL_COMPILE_STATUS, &status );
if( status == GL_FALSE )
{
fprintf( stderr, "fragment shader compilation failed\n" );
return 1;
}
program = glCreateProgram();
glAttachShader( program, vs );
glAttachShader( program, fs );
glBindAttribLocation( program, attrib_position, "i_position" );
glBindAttribLocation( program, attrib_color, "i_color" );
glLinkProgram( program );
glUseProgram( program );
glDisable( GL_DEPTH_TEST );
glClearColor( 0.5, 0.0, 0.0, 0.0 );
glViewport( 0, 0, width, height );
GLuint vao, vbo;
glGenVertexArrays( 1, &vao );
glGenBuffers( 1, &vbo );
glBindVertexArray( vao );
glBindBuffer( GL_ARRAY_BUFFER, vbo );
glEnableVertexAttribArray( attrib_position );
glEnableVertexAttribArray( attrib_color );
glVertexAttribPointer( attrib_color, 4, GL_FLOAT, GL_FALSE, sizeof( float ) * 6, 0 );
glVertexAttribPointer( attrib_position, 2, GL_FLOAT, GL_FALSE, sizeof( float ) * 6, ( void * )(4 * sizeof(float)) );
const GLfloat g_vertex_buffer_data[] = {
/* R, G, B, A, X, Y */
1, 0, 0, 1, 0, 0,
0, 1, 0, 1, width, 0,
0, 0, 1, 1, width, height,
1, 0, 0, 1, 0, 0,
0, 0, 1, 1, width, height,
1, 1, 1, 1, 0, height
};
glBufferData( GL_ARRAY_BUFFER, sizeof( g_vertex_buffer_data ), g_vertex_buffer_data, GL_STATIC_DRAW );
t_mat4x4 projection_matrix;
mat4x4_ortho( projection_matrix, 0.0f, (float)width, (float)height, 0.0f, 0.0f, 100.0f );
glUniformMatrix4fv( glGetUniformLocation( program, "u_projection_matrix" ), 1, GL_FALSE, projection_matrix );
for( ;; )
{
glClear( GL_COLOR_BUFFER_BIT );
SDL_Event event;
while( SDL_PollEvent( &event ) )
{
switch( event.type )
{
case SDL_KEYUP:
if( event.key.keysym.sym == SDLK_ESCAPE )
return 0;
break;
}
}
glBindVertexArray( vao );
glDrawArrays( GL_TRIANGLES, 0, 6 );
SDL_GL_SwapWindow( window );
SDL_Delay( 1 );
}
SDL_GL_DeleteContext( context );
SDL_DestroyWindow( window );
SDL_Quit();
return 0;
}
@RagnarDa
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And for others trying to run it in MacOS: change both ""#version 130\n" into "#version 330\n" or something similar and it will work (at least for me). Some sources suggest "#version 330 core\n"...

@chastitywhiterose
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This code is beautiful and compiles for me fine. I have no idea how it works yet but you are a genius for making this and sharing it with us all! Thanks a billion!

@Kitsune64
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Kitsune64 commented Mar 4, 2024 •
edited
Loading

Work with

#include <SDL2/SDL.h>
#include <SDL2/SDL_opengl.h>

-lSDL2 and -lGL in linker settings

Tested on Codeblocks under Debian (Linux)

@LainLayer
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Thanks for the only non-unhinged code example for this on the internet

@cascoxu
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cascoxu commented Feb 4, 2025 •
edited
Loading

For me to compile I need these headers:
#include <SDL.h>
#include <glew.h>
#include <SDL_opengl.h>
#include <string.h>
#include <stdio.h>

I don´t know what I am missing. But after adding these and compile the example only shows a red screen and no triangles are draw.

@ncake
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ncake commented Aug 8, 2025

I had to change the example like this to fix linker errors.

// ...

PFNGLCREATESHADERPROC glCreateShader;
PFNGLSHADERSOURCEPROC glShaderSource;
PFNGLCOMPILESHADERPROC glCompileShader;
PFNGLGETSHADERIVPROC glGetShaderiv;
PFNGLCREATEPROGRAMPROC glCreateProgram;
PFNGLATTACHSHADERPROC glAttachShader;
PFNGLBINDATTRIBLOCATIONPROC glBindAttribLocation;
PFNGLLINKPROGRAMPROC glLinkProgram;
PFNGLUSEPROGRAMPROC glUseProgram;
PFNGLGENVERTEXARRAYSPROC glGenVertexArrays;
PFNGLGENBUFFERSPROC glGenBuffers;
PFNGLBINDVERTEXARRAYPROC glBindVertexArray;
PFNGLBINDBUFFERPROC glBindBuffer;
PFNGLENABLEVERTEXATTRIBARRAYPROC glEnableVertexAttribArray;
PFNGLVERTEXATTRIBPOINTERPROC glVertexAttribPointer;
PFNGLBUFFERDATAPROC glBufferData;
PFNGLGETUNIFORMLOCATIONPROC glGetUniformLocation;
PFNGLUNIFORMMATRIX4FVPROC glUniformMatrix4fv;

// ...

int main( int argc, char * argv[] )
{
    // ...
    SDL_GLContext context = SDL_GL_CreateContext( window );

    #define LOAD_GL_FUNC(func, type) func = (type)SDL_GL_GetProcAddress(#func)
    LOAD_GL_FUNC(glCreateShader, PFNGLCREATESHADERPROC);
    LOAD_GL_FUNC(glShaderSource, PFNGLSHADERSOURCEPROC);
    LOAD_GL_FUNC(glCompileShader, PFNGLCOMPILESHADERPROC);
    LOAD_GL_FUNC(glGetShaderiv, PFNGLGETSHADERIVPROC);
    LOAD_GL_FUNC(glCreateProgram, PFNGLCREATEPROGRAMPROC);
    LOAD_GL_FUNC(glAttachShader, PFNGLATTACHSHADERPROC);
    LOAD_GL_FUNC(glBindAttribLocation, PFNGLBINDATTRIBLOCATIONPROC);
    LOAD_GL_FUNC(glLinkProgram, PFNGLLINKPROGRAMPROC);
    LOAD_GL_FUNC(glUseProgram, PFNGLUSEPROGRAMPROC);
    LOAD_GL_FUNC(glGenVertexArrays, PFNGLGENVERTEXARRAYSPROC);
    LOAD_GL_FUNC(glGenBuffers, PFNGLGENBUFFERSPROC);
    LOAD_GL_FUNC(glBindVertexArray, PFNGLBINDVERTEXARRAYPROC);
    LOAD_GL_FUNC(glBindBuffer, PFNGLBINDBUFFERPROC);
    LOAD_GL_FUNC(glEnableVertexAttribArray, PFNGLENABLEVERTEXATTRIBARRAYPROC);
    LOAD_GL_FUNC(glVertexAttribPointer, PFNGLVERTEXATTRIBPOINTERPROC);
    LOAD_GL_FUNC(glBufferData, PFNGLBUFFERDATAPROC);
    LOAD_GL_FUNC(glGetUniformLocation, PFNGLGETUNIFORMLOCATIONPROC);
    LOAD_GL_FUNC(glUniformMatrix4fv, PFNGLUNIFORMMATRIX4FVPROC);
    #undef LOAD_GL_FUNC
    // ...
}

@0xBAMA
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0xBAMA commented Aug 9, 2025 via email

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