Hi,
I'm totally new to 3D stuff. I thought I'd see if I could draw a rectangle
in perspective. For now it's face-on to the screen and doesn't move. I'm just trying to get used to the ideas and functions.
Here's the code I've got :-
| 1 | #include <allegro.h> |
| 2 | |
| 3 | struct vertex { |
| 4 | int x, y, z; |
| 5 | }; |
| 6 | |
| 7 | typedef struct vertex VERTEX; |
| 8 | |
| 9 | struct rectangle { |
| 10 | VERTEX rect_vertices[4]; /* vertices of rectangle relative to eachother */ |
| 11 | int x, y, z; /* co-ordinates of rectangle in world */ |
| 12 | VERTEX rect_vertices_world[4]; /* vertices of rectangle in world */ |
| 13 | }; |
| 14 | |
| 15 | typedef struct rectangle RECTANGLE; |
| 16 | |
| 17 | struct cartesian_point { |
| 18 | fixed x, y; |
| 19 | }; |
| 20 | |
| 21 | typedef struct cartesian_point C_POINT; |
| 22 | |
| 23 | /* all the vertices of the rectangle */ |
| 24 | VERTEX points[] = |
| 25 | { |
| 26 | { 0, 0, 0}, |
| 27 | {100, 0, 0}, |
| 28 | {100, 100, 0}, |
| 29 | { 0, 100, 0} |
| 30 | }; |
| 31 | |
| 32 | RECTANGLE r; |
| 33 | |
| 34 | |
| 35 | void init(void) |
| 36 | { |
| 37 | allegro_init(); |
| 38 | install_keyboard(); |
| 39 | set_color_depth(32); |
| 40 | if(set_gfx_mode(GFX_AUTODETECT, 640, 480, 0, 0) != 0) |
| 41 | { |
| 42 | set_gfx_mode(GFX_TEXT, 0, 0, 0, 0); |
| 43 | allegro_message("Unable to set graphics mode.\n"); |
| 44 | exit(1); |
| 45 | } |
| 46 | } |
| 47 | |
| 48 | |
| 49 | void draw_line(BITMAP *, C_POINT, C_POINT); |
| 50 | |
| 51 | void make_rect(void); |
| 52 | |
| 53 | |
| 54 | void draw_line(BITMAP *a, C_POINT point_1, C_POINT point_2) |
| 55 | { |
| 56 | int white = makecol32(255, 255, 255); |
| 57 | line(a, fixtoi(point_1.x), fixtoi(point_1.y), fixtoi(point_2.x), fixtoi(point_2.x), white); |
| 58 | } |
| 59 | |
| 60 | |
| 61 | void make_rect(void) |
| 62 | { |
| 63 | r.rect_vertices[0] = points[0]; |
| 64 | r.rect_vertices[1] = points[1]; |
| 65 | r.rect_vertices[2] = points[2]; |
| 66 | r.rect_vertices[3] = points[3]; |
| 67 | |
| 68 | r.x = 0; |
| 69 | r.y = 0; |
| 70 | r.z = 200; |
| 71 | } |
| 72 | |
| 73 | |
| 74 | |
| 75 | int main() |
| 76 | { |
| 77 | int i; |
| 78 | |
| 79 | C_POINT rect_points_2d[4]; /* Somewhere to store the translated points of the |
| 80 | rectangle. */ |
| 81 | |
| 82 | BITMAP *buffer; |
| 83 | |
| 84 | init(); |
| 85 | |
| 86 | buffer = create_bitmap(640, 480); |
| 87 | |
| 88 | set_projection_viewport(0, 0, SCREEN_W, SCREEN_H); |
| 89 | |
| 90 | /* work out where vertices are in the world */ |
| 91 | |
| 92 | for(i = 0; i < 4; ++i) |
| 93 | { |
| 94 | r.rect_vertices_world<i>.x = r.rect_vertices<i>.x + r.x; |
| 95 | r.rect_vertices_world<i>.y = r.rect_vertices<i>.y + r.y; |
| 96 | r.rect_vertices_world<i>.z = r.rect_vertices<i>.z + r.z; |
| 97 | } |
| 98 | |
| 99 | /* translate the shapes into cartesian coordinates */ |
| 100 | |
| 101 | for(i = 0; i < 4; ++i) |
| 102 | { |
| 103 | persp_project(itofix(r.rect_vertices_world<i>.x), |
| 104 | itofix(r.rect_vertices_world<i>.y), |
| 105 | itofix(r.rect_vertices_world<i>.z), |
| 106 | &rect_points_2d<i>.x, |
| 107 | &rect_points_2d<i>.y); |
| 108 | } |
| 109 | |
| 110 | /* Draw lines between connecting points of the rectangle. */ |
| 111 | |
| 112 | draw_line(buffer, rect_points_2d[0], rect_points_2d[1]); |
| 113 | draw_line(buffer, rect_points_2d[1], rect_points_2d[2]); |
| 114 | draw_line(buffer, rect_points_2d[3], rect_points_2d[4]); |
| 115 | draw_line(buffer, rect_points_2d[4], rect_points_2d[0]); |
| 116 | |
| 117 | blit(buffer, screen, 0, 0, 0, 0, 640, 480); |
| 118 | readkey(); |
| 119 | |
| 120 | return 0; |
| 121 | } |
| 122 | END_OF_MAIN() |
All it does is draw a diagonal line across the screen.
I put plently of comments in to make it easy to understand.
Can someone help me understand what I'm doing wrong please ?
[edit]
sorry, It'd help if I'd have spent a bit more time checking for obvious mistakes 
