#include <allegro.h>
#include <alleggl.h>

// The texture handles
GLuint Tex[3];

// The texture filenames
const char* TexFiles[3] =
{
    "layer0.bmp",
    "layer1.bmp",
    "layer2.bmp"
};

// The font we will be using
FONT* Font;

// Possible source factors
const int NumSourceFactors = 9;
const int SourceFactors[NumSourceFactors] =
{
    GL_ONE, GL_ZERO, GL_DST_COLOR, GL_ONE_MINUS_DST_COLOR,
    GL_SRC_ALPHA_SATURATE, GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_DST_ALPHA,
    GL_ONE_MINUS_DST_ALPHA
};

// Source factor names
const char* SourceNames[NumSourceFactors] =
{
    "GL_ONE", "GL_ZERO", "GL_DST_COLOR", "GL_ONE_MINUS_DST_COLOR",
    "GL_SRC_ALPHA_SATURATE", "GL_SRC_ALPHA", "GL_ONE_MINUS_SRC_ALPHA",
    "GL_DST_ALPHA", "GL_ONE_MINUS_DST_ALPHA"
};

// Possible destination factors
const int NumDestFactors = 8;
const int DestFactors[NumDestFactors] =
{
    GL_ONE, GL_ZERO, GL_SRC_COLOR, GL_ONE_MINUS_SRC_COLOR, GL_SRC_ALPHA,
    GL_ONE_MINUS_SRC_ALPHA, GL_DST_ALPHA, GL_ONE_MINUS_DST_ALPHA
};

// Destination factor names
const char* DestNames[NumDestFactors] =
{
    "GL_ONE", "GL_ZERO", "GL_SRC_COLOR", "GL_ONE_MINUS_SRC_COLOR",
    "GL_SRC_ALPHA", "GL_ONE_MINUS_SRC_ALPHA", "GL_DST_ALPHA",
    "GL_ONE_MINUS_DST_ALPHA"
};

void Init()
{
    // Start up Allegro and AllegroGL systems
    allegro_init();
    install_allegro_gl();
    install_keyboard();

    // Set the color depth to 32 - needed for some blending modes
    allegro_gl_set(AGL_COLOR_DEPTH, 32);
    allegro_gl_set(AGL_SUGGEST, AGL_COLOR_DEPTH);

    // Set up a suitable viewing window
    set_color_depth(32);
    set_gfx_mode(GFX_OPENGL_WINDOWED, 256, 300, 0, 0);

    // Enable texturing and blending
    glEnable(GL_TEXTURE_2D);
    glEnable(GL_BLEND);

    // We are using 24 bit textures in this case.
    allegro_gl_set_texture_format(GL_RGB8);

    // Load the textures
    for(int i = 0; i < 3; i++)
    {
        BITMAP* temp_bmp = load_bitmap(TexFiles[i], 0);
        Tex[i] = allegro_gl_make_texture(temp_bmp);
        glTexEnvi(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        glTexEnvi(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        destroy_bitmap(temp_bmp);
    }

    // Convert the default Allegro font to an AllegroGL font
    Font = allegro_gl_convert_allegro_font(font, AGL_FONT_TYPE_TEXTURED, 1.0);

    // Set up coordinates that mimic a per-pixel style
    glOrtho(0, SCREEN_W, 0, SCREEN_H, 1.0, -1.0);

    // Set the background color to black
    glClearColor(0.0, 0.0, 0.0, 0.0);
}

int main()
{
    Init();

    bool quit = false;
    int src_f = 0, dst_f = 0;
    float layer_alpha[3] = { 1.0, 0.8, 0.6 };
    int key = 0;

    while(!quit)
    {
        // Clear the window
        glClear(GL_COLOR_BUFFER_BIT);

        // Draw the three layers
        for(int i = 0; i < 3; i++)
        {
            if(i == 0)
                glBlendFunc(GL_ONE, GL_ZERO);
            else if(i == 1)
                glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
            else
                glBlendFunc(SourceFactors[src_f], DestFactors[dst_f]);
            glBindTexture(GL_TEXTURE_2D, Tex[i]);
            glBegin(GL_QUADS);
                glColor4f(1.0, 1.0, 1.0, layer_alpha[i]);
                glTexCoord2i(0, 0);
                glVertex2i(0, 0);
                glTexCoord2i(1, 0);
                glVertex2i(255, 0);
                glTexCoord2i(1, 1);
                glVertex2i(255, 255);
                glTexCoord2i(0, 1);
                glVertex2i(0, 255);
            glEnd();
        }

        glBlendFunc(GL_ONE, GL_ZERO);
        allegro_gl_printf(Font, 0, 300, 0, makeacol(255, 255, 255, 255),
            "SRC: %s", SourceNames[src_f]);
        allegro_gl_printf(Font, 0, 290, 0, makeacol(255, 255, 255, 255),
            "DST: %s", DestNames[dst_f]);
        allegro_gl_printf(Font, 0, 278, 0, makeacol(255, 255, 255, 255),
            "Top layer alpha: %f", layer_alpha[2]);
        allegro_gl_printf(Font, 0, 268, 0, makeacol(255, 255, 255, 255),
            "Bottom layer alpha: %f", layer_alpha[1]);

        glFlush();

        // Wait for a keypress
        clear_keybuf();
        key = readkey() >> 8;

        // Cycle through the different blending modes.
        if(key == KEY_S)    src_f++;
        if(key == KEY_D)    dst_f++;
        if(src_f >= NumSourceFactors)   { src_f = 0; dst_f++; }
        if(dst_f >= NumDestFactors)     { dst_f = 0; }

        // Adjust alpha of the two top layers.
        if(key == KEY_RIGHT)
            layer_alpha[2] += 0.05;
        if(key == KEY_LEFT)
            layer_alpha[2] -= 0.05;
        if(key == KEY_UP)
            layer_alpha[1] += 0.05;
        if(key == KEY_DOWN)
            layer_alpha[1] -= 0.05;

        // Quit if ESC is pressed
        if(key == KEY_ESC)
        {
            quit = true;
        }
    }

    return 0;
}
END_OF_MAIN();