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// Built from glbook/hello triange and sdl_ogl, see details there
#include "SDL/SDL.h"
#include "SDL/SDL_image.h"
#include "SDL/SDL_opengl.h"
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
GLuint programObject;
int width = 512;
int height = 256;
GLuint LoadShader ( GLenum type, const char *shaderSrc )
{
GLuint shader;
GLint compiled;
shader = glCreateShader ( type );
if ( shader == 0 )
return 0;
glShaderSource ( shader, 1, &shaderSrc, NULL );
glCompileShader ( shader );
glGetShaderiv ( shader, GL_COMPILE_STATUS, &compiled );
if ( !compiled )
{
GLint infoLen = 0;
glGetShaderiv ( shader, GL_INFO_LOG_LENGTH, &infoLen );
if ( infoLen > 1 )
{
char* infoLog = malloc (sizeof(char) * infoLen );
glGetShaderInfoLog ( shader, infoLen, NULL, infoLog );
printf ( "Error compiling shader:\n%s\n", infoLog );
free ( infoLog );
}
glDeleteShader ( shader );
return 0;
}
return shader;
}
int Init ()
{
GLbyte vShaderStr[] =
"attribute vec4 vPosition; \n"
"void main() \n"
"{ \n"
" gl_Position = vPosition; \n"
"} \n";
GLbyte fShaderStr[] =
"precision mediump float;\n"\
"void main() \n"
"{ \n"
" gl_FragColor = vec4 ( 0.0, 0.0, 1.0, 1.0 );\n"
"} \n";
GLuint vertexShader;
GLuint fragmentShader;
GLint linked;
vertexShader = LoadShader ( GL_VERTEX_SHADER, vShaderStr );
fragmentShader = LoadShader ( GL_FRAGMENT_SHADER, fShaderStr );
programObject = glCreateProgram ( );
if ( programObject == 0 )
return 0;
glAttachShader ( programObject, vertexShader );
glAttachShader ( programObject, fragmentShader );
glBindAttribLocation ( programObject, 0, "vPosition" );
glLinkProgram ( programObject );
glGetProgramiv ( programObject, GL_LINK_STATUS, &linked );
if ( !linked )
{
GLint infoLen = 0;
glGetProgramiv ( programObject, GL_INFO_LOG_LENGTH, &infoLen );
if ( infoLen > 1 )
{
char* infoLog = malloc (sizeof(char) * infoLen );
glGetProgramInfoLog ( programObject, infoLen, NULL, infoLog );
printf ( "Error linking program:\n%s\n", infoLog );
free ( infoLog );
}
glDeleteProgram ( programObject );
return GL_FALSE;
}
glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f );
return GL_TRUE;
}
///
// Draw a triangle using the shader pair created in Init()
//
void Draw ()
{
GLfloat vVertices[] = { 0.0f, 0.5f, 0.0f,
-0.5f, -0.5f, 0.0f,
0.5f, -0.5f, 0.0f };
// No clientside arrays, so do this in a webgl-friendly manner
GLuint vertexPosObject;
glGenBuffers(1, &vertexPosObject);
glBindBuffer(GL_ARRAY_BUFFER, vertexPosObject);
glBufferData(GL_ARRAY_BUFFER, 9*4, vVertices, GL_STATIC_DRAW);
glViewport ( 0, 0, width, height );
glClear ( GL_COLOR_BUFFER_BIT );
glUseProgram ( programObject );
glBindBuffer(GL_ARRAY_BUFFER, vertexPosObject);
glVertexAttribPointer(0 /* ? */, 3, GL_FLOAT, 0, 0, 0);
glEnableVertexAttribArray(0);
glDrawArrays ( GL_TRIANGLES, 0, 3 );
}
void Verify() {
unsigned char *data = malloc(width*height*4 + 16);
int *last = (int*)(data + width*height*4 - 4);
int *after = (int*)(data + width*height*4);
*last = 0xdeadbeef;
*after = 0x12345678;
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, data);
assert(*last != 0xdeadbeef); // should overwrite the buffer to the end
assert(*after == 0x12345678); // nothing should be written afterwards!
// Should see some blue, and nothing else
int seen = 0;
int ok = 1;
for (int x = 0; x < width*height; x++) {
seen = seen || data[x*4+2] != 0;
ok = ok && (data[x*4+0] == 0);
ok = ok && (data[x*4+1] == 0);
}
int result = seen && ok;
REPORT_RESULT();
}
int main(int argc, char *argv[])
{
SDL_Surface *screen;
if ( SDL_Init(SDL_INIT_VIDEO) != 0 ) {
printf("Unable to initialize SDL: %s\n", SDL_GetError());
return 1;
}
screen = SDL_SetVideoMode(width, height, 32, SDL_OPENGL);
if (!screen) {
printf("Unable to set video mode: %s\n", SDL_GetError());
return 1;
}
Init();
Draw();
Verify();
return 0;
}
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