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

First, follow the tutorial ScratchBox2 cross compiling with SDL to set up the cross compilation environment.

Next, copy the source below into a file doomtriangle.c

Now run scratchbox2 with the webos / pre mapping file:

$ sb2 -M /srv/preware/cross-compile/staging/mapping-armv7

You will get a different prompt indicating you are in a scratchbox shell, like:

[SB2 mapping-armv7 armv7] $

Now just

gcc -Wl,-rpath-link=/usr/local/lib -I/usr/local/include/SDL -L/usr/local/lib -o doomtriangle doomtriangle.c -lSDL -lGLESv2

Now, copy the resulting binary doomtriangle to your pre and run it.

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;
}