ref: a0bc995332afdd4b693347cfae94694e6c601aed
dir: /screen.c/
/*
* Ball - a first attempt at Plan 9 graphics programming
* Author: nspool
* Date: 2013-02-19
* Licence: MIT
* /
/* Build with '8c -FTVw ball.c && 8l -o ball ball.8' */
#include <u.h>
#include <libc.h>
#include <draw.h>
#include <event.h>
void moveball(void);
void initball(void);
Image *ball;
Point p;
/* Menus */
char *buttons[] = {"exit", 0};
Menu menu = { buttons };
/* Radius of ball */
int r = 20;
int borderWidth = 4;
/* Change direction of ball if collision
* else move the ball and draw to screen
* The new ball image draws over the previous image
* so there is no need to redraw the whole screen */
void
moveball()
{
static Point bp={6, 6}; /* Ball Position */
static double Δi=4, Δj=4;
/* Collision detection */
if(bp.x > p.x - (r*3) || bp.x < -r) Δi = Δi*-1;
if(bp.y > p.y - (r*3) || bp.y < -r) Δj = Δj*-1;
/* Increment ball position */
bp.x = bp.x + Δi;
bp.y = bp.y + Δj;
draw(screen, rectaddpt(screen->r, bp), ball, nil, ZP);
}
/* Graphics library requires this function */
void
eresized(int new)
{
if(new && getwindow(display, Refnone) < 0)
sysfatal("can't reattach to window");
/* Store new screen coordinates for collision detection */
p = Pt(Dx(screen->r), Dy(screen->r));
/* Draw the background DWhite */
draw(screen, insetrect(screen->r, borderWidth),
allocimage(display, Rect(0, 0, 1, 1), screen->chan, 1, DWhite),
nil, ZP);
}
/* Draw red ball inside a square of white background
* When ball is drawn at new position, background will
* blot out the previous image */
void
initball()
{
Image *brush;
brush=allocimage(display, Rect(0,0,1,1), CMAP8, 1, DRed);
ball=allocimage(display, (Rectangle){(Point){0,0},(Point){r*4,r*4}},
screen->chan, 0, DWhite);
fillellipse(ball, (Point){r*2,r*2}, r, r, brush, ZP);
}
void
initscreen(int argc, char *argv[])
{
USED(argc, argv);
Event ev;
int e, timer;
/* Initiate graphics and mouse */
if(initdraw(nil, nil, "bouncing ball demo") < 0)
sysfatal("initdraw failed: %r");
einit(Emouse);
/* Start our timer
* move the ball every 5 milliseconds
* unless there is an Emouse event */
timer = etimer(0, 5);
/* Simulate a resize event to draw the background
* and acquire the screen dimensions */
eresized(0);
initball();
/* Main event loop */
for(;;)
{
e = event(&ev);
/* If there is a mouse event, the rightmost button
* pressed and the first menu option selected
* then exit.. */
if( (e == Emouse) &&
(ev.mouse.buttons & 4) &&
(emenuhit(3, &ev.mouse, &menu) == 0)) exits(nil);
else
if(e == timer)
moveball();
}
}