OpenGL Triangle of Doom

The demo app

This app is loosely based on a an OpenGL example from the maemo project and is ported from X11 OpenGL code to SDL to function in webos

Assuming that you have installed the Scratchbox2 cross compiling environment as described in the Scratchbox2 page then all you will have to do is go to that install and:

Then compile the app this way:

gcc -o doomtriangle doomtriangle.c  -I/usr/local/include/SDL -lSDL -lGLESv2

And exit the chroot, cd to the directory in your debian filesystem where you built the binary, and run it like:

./doomtriangle

doomtriangle.c

#include <stdio.h>
#include <stdlib.h>
#include "SDL.h"
#include "SDL_opengles.h"
#include "SDL_video.h"
#include <math.h>
#include <sys/time.h>
#include <unistd.h>
#include <string.h>

const char* vertexSrc = "attribute vec4 position; varying mediump vec2 pos; void main() { gl_Position = position; pos = position.xy; }";
const char* fragmentSrc = "varying mediump vec2 pos; uniform mediump float phase; void main() { gl_FragColor = vec4(1, 1, 1, 1) * sin((pos.x * pos.x + pos.y * pos.y) * 40.0 + phase); }";
//const char* fragmentSrc = "varying mediump vec2 pos; uniform mediump float phase; void main() { gl_FragColor = vec4(1, 1, 1, 1) * step(pos.x * pos.x + pos.y * pos.y, phase * 0.2); }";

void printShaderInfoLog(GLuint shader) {
    GLint length;
    glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &length);
    if(length) {
        char* buffer = (char *)malloc( sizeof(char) * length ) ;
        glGetShaderInfoLog(shader, length, NULL, buffer);
        printf("%s", buffer);
        free( buffer ) ;
        GLint success;
        glGetShaderiv(shader, GL_COMPILE_STATUS, &success);
        if(success != GL_TRUE) {
            exit(1);
        }
    }
}

GLuint createShader(GLenum type, const char* pSource) {
    GLuint shader = glCreateShader(type);
    glShaderSource(shader, 1, &pSource, NULL);
    glCompileShader(shader);
    printShaderInfoLog(shader);
    return shader;
}

int phaseLocation ;

const float vertexArray[] = {
    0, -1, 0, 1,
    1, 1, 0, 1,
    -1, 1, 0, 1
};

#define false 0
#define true 1
#define bool int

void render() {
        static float offset = 0;

        glViewport(0, 0, 320, 480 ) ;
        glClearColor(0, 1, 0, 1);
        glClear(GL_COLOR_BUFFER_BIT);
        
        glUniform1f(phaseLocation, offset);
        
        glVertexAttribPointer(0, 4, GL_FLOAT, false, 0, vertexArray);
        glEnableVertexAttribArray(0);
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 3);
        
        SDL_GL_SwapBuffers( ) ;
        
        offset = fmodf(offset + 0.2, 2*3.141f);
}

int main() {

    if( SDL_Init( SDL_INIT_VIDEO ) < 0 ) {
        fprintf( stderr, "Couldn't initialize SDL: %s\n", SDL_GetError() ) ;
        exit( 1 ) ;
    }

    if ( SDL_SetVideoMode( 320, 480, 32, SDL_OPENGLES ) == NULL ) {
        fprintf(stderr, "Couldn't set GL mode: %s\n", SDL_GetError());
        SDL_Quit();
        exit(1);
    }

    printf("Screen BPP: %d\n", SDL_GetVideoSurface()->format->BitsPerPixel);
    printf("\n");
    printf( "Vendor     : %s\n", glGetString( GL_VENDOR ) );
    printf( "Renderer   : %s\n", glGetString( GL_RENDERER ) );
    printf( "Version    : %s\n", glGetString( GL_VERSION ) );
    printf( "Extensions : %s\n", glGetString( GL_EXTENSIONS ) );
    printf("\n");

    GLuint shaderProgram = glCreateProgram();
    GLuint vertexShader = createShader(GL_VERTEX_SHADER, vertexSrc);
    GLuint fragmentShader = createShader(GL_FRAGMENT_SHADER, fragmentSrc);
    
    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    
    glLinkProgram(shaderProgram);
    
    glUseProgram(shaderProgram);
    
    phaseLocation = glGetUniformLocation(shaderProgram, "phase");
    if(phaseLocation < 0) {
        printf("Unable to get uniform location\n");
        return 1;
    }
    
    bool quit = false;
    
    //timeval startTime;
    //timezone tz;
    //gettimeofday(&startTime, &tz);
    int numFrames = 0;
    
    while(!quit) {
        SDL_Event event ;
        while( SDL_PollEvent( &event ) ) {
            if( event.type == SDL_KEYDOWN && event.key.keysym.sym == SDLK_ESCAPE ) quit = 1 ;
        }
                render();
                numFrames++;
                if(numFrames % 100 == 0) {
                    //timeval now;
                    //gettimeofday(&now, &tz);
                    //float delta = now.tv_sec - startTime.tv_sec + (now.tv_usec - startTime.tv_usec) * 0.000001f;
                    //printf("fps: %f\n", numFrames / delta);
                }
    }
    return 0;
}