Fast Way To Check If Certain Pixel is Inside Certain Surface

SDL Development
1

Hi, i’m working on a particle engine (pixel-based, for now) and i’d
implement the following code for checking if the pixel is inside that
Certain Surface:

for(int i=surface->clip_rect.x; iclip_rect.w; i++)
for(int j=surface->clip_rect.y; jclip_rect.h; j++)
if(particle.x == i && particle.y == j) do something.

But this carried me bigs “delays” whenever its executed.
Has somebody a better way to doing it?.

Thx, and sorry for my english, not native.–
Leandro Ostera,
Caelis Interactive

2

Hi Phantom,

Just FYI the SDL list is not used for programming techniques so much, it’s
mostly for help with sdl specific questions. A much better list for that is
at gameprogrammer.com.

But yes, there is a much better way than doing what you are doing!

Instead of checking every x and y of a surface to see if it matches a
particle’s x and y, do this:

If((particle.x>=surface->clip_rect.x)&&(particle.x<=(surface->clip_rect.x+su
rface->clip_rect.w))&&

(particle.y>=surface->clip_rect.y)&&(particle.y<=(surface->clip_rect.y+surfa
ce->clip_rect.h)))

{

//do something

}

This way instead of testing each and every pixel on the surface, you are
just checking to see mathematically if the pixel is inside the other surface
or not._____

From: sdl-bounces+atrix2=cox.net@libsdl.org
[mailto:sdl-bounces+atrix2=cox.net at libsdl.org] On Behalf Of Phantom Lord
Sent: Monday, July 03, 2006 5:19 PM
To: A list for developers using the SDL library. (includes SDL-announce)
Subject: [SDL] Fast Way To Check If Certain Pixel is Inside Certain Surface

Hi, i’m working on a particle engine (pixel-based, for now) and i’d
implement the following code for checking if the pixel is inside that
Certain Surface:

for(int i=surface->clip_rect.x; iclip_rect.w; i++)

for(int j=surface->clip_rect.y; jclip_rect.h; j++)

  if(particle.x == i && particle.y == j) do something.

But this carried me bigs “delays” whenever its executed.

Has somebody a better way to doing it?.

Thx, and sorry for my english, not native.

–
Leandro Ostera,
Caelis Interactive

3

Phantom Lord wrote:

Hi, i’m working on a particle engine (pixel-based, for now) and i’d
implement the following code for checking if the pixel is inside that
Certain Surface:

for(int i=surface->clip_rect.x; iclip_rect.w; i++)
for(int j=surface->clip_rect.y; jclip_rect.h; j++)
if(particle.x == i && particle.y == j) do something.

if ((particle.x >= surface->clip_rect.x) &&
(particle.x < surface->clip_rect.x + surface->clip_rect.w) &&
(particle.y >= surface->clip_rect.y) &&
(particle.y < surface->clip_rect.y + surface->clip_rect.h)) {
do_something();
}

  .bill
4

Thx guys.

2006/7/4, Vassilis Virvilis :>

Phantom Lord wrote:

Hi, i’m working on a particle engine (pixel-based, for now) and i’d
implement the following code for checking if the pixel is inside that
Certain Surface:

for(int i=surface->clip_rect.x; iclip_rect.w; i++)
for(int j=surface->clip_rect.y; jclip_rect.h; j++)
if(particle.x == i && particle.y == j) do something.

if ((particle.x >= surface->clip_rect.x) &&
(particle.x < surface->clip_rect.x + surface->clip_rect.w) &&
(particle.y >= surface->clip_rect.y) &&
(particle.y < surface->clip_rect.y + surface->clip_rect.h)) {
do_something();
}

 .bill

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–
Phantom Lord
Caelis Studios —> From Gods Hands To Yours