allegro-projection-test.c

#include <math.h>
#include <assert.h>
#include <stdio.h>
#include <allegro5/allegro.h>
#include <allegro5/allegro_primitives.h>
#include <allegro5/allegro_native_dialog.h>

int main() {
  al_init();
  al_install_keyboard();
  al_init_native_dialog_addon();
  al_init_primitives_addon();

  al_set_new_display_flags(ALLEGRO_WINDOWED | ALLEGRO_OPENGL);
//  al_set_new_display_option(ALLEGRO_REQUIRE, ALLEGRO_COMPATIBLE_DISPLAY, 1);
  al_set_new_display_option(ALLEGRO_SUGGEST, ALLEGRO_DEPTH_SIZE,         16);
  //al_set_new_display_option(ALLEGRO_REQUIRE, ALLEGRO_SAMPLE_BUFFERS,     1);
  //al_set_new_display_option(ALLEGRO_REQUIRE, ALLEGRO_SAMPLES,            8);
  ALLEGRO_DISPLAY* display = al_create_display(1024, 768);
  assert(display);
  
  al_set_target_bitmap(al_get_backbuffer(display));
  al_clear_depth_buffer(1);
  al_clear_to_color(al_map_rgb(0,0,0));
  
  ALLEGRO_TRANSFORM camera;
  al_build_camera_transform(&camera, 0, 128, -512, 0, 128, -511, 0, 1, 0);
  
  ALLEGRO_TRANSFORM default_regular;
  ALLEGRO_TRANSFORM default_projection;
  al_copy_transform(&default_regular,    al_get_current_transform());
  al_copy_transform(&default_projection, al_get_current_projection_transform());
  
  ALLEGRO_TRANSFORM projection;
  float proportions = (float)1024 / (float)768;
  float angle       = 90;
  float f           = tanf((angle * ALLEGRO_PI / 180) / 2);
  al_identity_transform(&projection);
  al_perspective_transform(&projection,
    -1 * proportions * f,  1 * f, 1,
     1 * proportions * f, -1 * f, 10000);
  
  al_set_render_state(ALLEGRO_DEPTH_TEST, 1);
  al_use_projection_transform(&projection);
  
  ALLEGRO_TRANSFORM rectangle_transform;
  al_identity_transform(&rectangle_transform);
  al_translate_transform_3d(&rectangle_transform, 0, 0, 0);
  al_rotate_transform_3d(&rectangle_transform, 1, 0, 0, (float) ALLEGRO_PI / 2);
  
  ALLEGRO_TRANSFORM camera_rectangle_transform;
  al_copy_transform(&camera_rectangle_transform, &rectangle_transform);
  al_compose_transform(&camera_rectangle_transform, &camera);
  
  al_use_transform(&camera_rectangle_transform);
  
  ALLEGRO_COLOR grey = al_map_rgba(100, 100, 100, 100);
  al_draw_filled_rectangle(-128, -128, 128, 128, grey); // around (0,0,0)
  
  al_use_transform(&default_regular);
  al_use_projection_transform(&default_projection);
  
  float x = 0;
  float y = 0;
  float z = 0;
  
  al_transform_coordinates_3d(&camera_rectangle_transform, &x, &y, &z);
  printf("vector 3d: x:%f y:%f z:%f\n", x, y, z);
  
  al_transform_coordinates_3d_projective(&projection, &x, &y, &z);
  printf("vector 3d: x:%f y:%f z:%f\n", x, y, z);
  
  ALLEGRO_COLOR red = al_map_rgb_f(1,0,0);
  al_draw_filled_rectangle(x - 4, y - 4, x + 4, y + 4, red);
  
  x += 512;
  y += 384;
  printf("vector 3d: x:%f y:%f z:%f\n", x, y, z);
  
  ALLEGRO_COLOR green = al_map_rgb_f(0,1,0);
  al_draw_filled_rectangle(x - 4, y - 4, x + 4, y + 4, green);
  
  al_flip_display();
  
  while (true) sleep(1000);
  
  al_destroy_display(display);
}