c++ - Weirdly behaving pixel by pixel 3d graphing program [Faster drawing by dragging the window] -


so coding simple 3d graphing program in c++ using allegro 4 libraries. made in simple way, drawing pixel pixel. usually, putting single pixels on screen pretty slow because of how allegro works , plot graph in resolution of 640x480 have wait minute or two.

so rendering image buddy show , dragging windows around have screenshot , discovered dragging window rendering picture, speeds long hold window. 2 minutes draws in 10 seconds.

what's cause of bizzare behavior? related windows' windows or caused allegro itself? there explanation this?

screenshot

also code

#include <allegro.h> #include <iostream> #include <math.h>  using namespace std;  float max_z = 1; float min_z =-1; float scale =50;  inline void init(unsigned int width, unsigned int height) {     allegro_init();     set_color_depth(24);     set_gfx_mode(gfx_autodetect_windowed, width, height, 0, 0);      install_timer();     install_keyboard();     install_mouse(); }  inline void deinit() {     clear_keybuf();     allegro_exit(); }  int get_z_color (float z) {     if (z >= 0)     {         return makecol(255, (z/max_z)*255, (z/max_z)*255);     }     else     {         return makecol(255 - (z/min_z)*255,0, 0);     } }  float get_z (float x, float y) {     return sin(sqrt(pow(x,2)+pow(y,2))); }  float int_to_float (int a) {     return a; }  int main() {     unsigned int res_width, res_height;      cout << "window size (w,h): ";     cin >> res_width >> res_height;     cout << endl << "initiating in " << res_width << "x" << res_height << " resolution..." << endl;      init(res_width,res_height);      cout << "success! drawing graph..." << endl;      (int y=0; y<res_height; y++)     {         (int x=0; x<res_width; x++)         {             float valued_x = (int_to_float(x)-(int_to_float(res_width)/2))/scale;             float valued_y = (int_to_float(-y)+(int_to_float(res_height)/2))/scale;             _putpixel24(screen,x,y,get_z_color(get_z(valued_x,valued_y)));             //cout << "drawing (" << valued_x << "," << valued_y << ")" << endl;         }     }      cout << "graph drawn." << endl;      cin >> new char;      cout << "closing...";      deinit();     return 0; } end_of_main()

drawing on screen surfaces, whatever library you're using, costly operation.

i never used allegro (i'm using sdl), guess windows redraws screen surface each time single pixel put on it, , dragging windows around, prevent redrawing happening.

if want program dramatic increase in performance, should draw off-screen surface, , blit entire surface screen surface once drawing on (this basic double buffering technique).

like said, never used allegro, gather, :

int main() {   unsigned int res_width, res_height;    cout << "window size (w,h): ";   cin >> res_width >> res_height;   cout << endl << "initiating in " << res_width << "x" << res_height << " resolution..." << endl;    init(res_width,res_height);    bitmap *temporarybitmap = create_bitmap(res_width, res_height);    cout << "success! drawing graph..." << endl;    (int y=0; y<res_height; y++)   {     (int x=0; x<res_width; x++)     {         float valued_x = (int_to_float(x)-(int_to_float(res_width)/2))/scale;         float valued_y = (int_to_float(-y)+(int_to_float(res_height)/2))/scale;         _putpixel24(temporarybitmap,x,y,get_z_color(get_z(valued_x,valued_y)));         //cout << "drawing (" << valued_x << "," << valued_y << ")" << endl;     }   }    blit(temporarybitmap, screen, 0, 0, 0, 0, temporarybitmap->w, temporarybitmap->h);    cout << "graph drawn." << endl;    cin >> new char;    cout << "closing...";    destroy_bitmap(temporarybitmap);    deinit();   return 0; }

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