TheGameCreators - CodeBase - Nearly pixel perfect sprite collision detection

Category: Sprite

Version: 1.0

Information

Uploaded: 11th Oct 2003 07:23

Modified: 15th Oct 2003 10:14

Author: haggisman

Summary

It works for any sprite, no matter what the rotation or scaling of the sprites it will still retain the near pixel perfect collision.

Full Description

Everything needed can be found in the zip, both some simple code showing the collision detection routine and also the code for creating the collision template for the sprites.<br /> <br /> The collision template creator simply creates an outline of a sprite on the edge between the opaque and transparent areas, the outline is used to generate lines that the collision will be detected against. Normals will also be generated at this point, which will eventually allow me to make collision responses IE sliding/bouncing/sticking collision.<br /> <br /> The Simple example just shows the collision routine very basically between two objects. The one being controlled can be moved rotated and scaled and still produce accurate collision. It works on the very basic principle that if lines of either shape intersect then there is a collision. There is still a lot of optimization to do but I believe its still fast enough in its current state for some nice 2d games.

DarkBASIC Professional Source Code

` This code was downloaded from The Game Creators

` It is reproduced here with full permission

` http://www.thegamecreators.com

Rem This is just sample source, it will most likely NOT work. For the actual source

Rem download the attached zip file!

Rem ***** Main Source File *****

rem Standard Setup Code

sync on : sync rate 0 : color backdrop rgb(0,0,0) : hide mouse

set text font "arial" : set text size 24 : set text transparent : set text to bold

rem Variables

global Uvector=1

global Vvector=2

global Wvector=3

global Normal_length#

Sprite_number=2

control=2

Highest_possible=1000

Normal_length#=1.0

rem Types

Type Sprite_data line_number as integer X as integer Y as integer Orig_Radius as float Radius as float Mass as integer endtype

Type normal_data X as float Y as float endtype

Type line_data X1 as float Y1 as float X2 as float Y2 as float endtype

rem Arrays

global Dim User_Sprite(Sprite_number) as Sprite_data

global Dim lines(Sprite_number, Highest_possible) as line_data

global Dim T_lines(Sprite_number, Highest_possible) as line_data

global Dim normals(Sprite_number, Highest_possible) as normal_data

rem Vectors

rf=make vector2(Uvector)

rf=make vector2(Vvector)

rf=make vector2(Wvector)

rem Firstly load the sprites in

Load_Sprite("ShapeA", ".bmp", 1)

Load_Sprite("ShapeB", ".bmp", 2)

rem Set some nice sprite positions

User_sprite(1).X=512 : User_sprite(1).Y=384

User_sprite(2).X=600 : User_sprite(2).Y=350

Transform_collision_coords(1)

Transform_collision_coords(2)

rem Main loop

`control the strange shape

User_sprite(control).X=mousex()

User_sprite(control).Y=mousey()

if mouseclick()=1 then rotate sprite control, (sprite angle(control) + 2)

if mouseclick()=2 then rotate sprite control, (sprite angle(control) - 2)

if upkey()=1 then stretch sprite control, sprite scale x(control), sprite scale y(control)+5

if downkey()=1 and sprite scale y(control)>10 then stretch sprite control, sprite scale x(control), sprite scale y(control)-5

if leftkey()=1 and sprite scale x(control)>10 then stretch sprite control, sprite scale x(control)-5, sprite scale y(control)

if rightkey()=1 then stretch sprite control, sprite scale x(control)+5, sprite scale y(control)

Transform_collision_coords(control)

`check for collision

for x=1 to 2

collision_return=0

`need distance check with bounding spheres.

if x<>control

collision_return=Sprite_Collision_Check(x, control)

endif

if collision_return>0 then collision_return=x : exit

next x

`Paste the sprites to screen

for x=1 to Sprite_number

if x<>control

paste sprite x, User_sprite(x).X, User_sprite(x).Y

endif

next x

paste sprite control, User_sprite(control).X, User_sprite(control).Y

`draw all the lines for puropses of debugging

`for x=1 to sprite_number

`draw_lines_on(x)

`next x

center Text 512, 0, "Mouse moves the red object; Mouse buttons rotate it; Arrow keys change scale"

center Text 512, 24, "COLLISION RESULT :- " + str$(collision_return)

Text 0, 0, "FPS: " + str$(screen fps())

Sync

Loop

`*******************************************************************************************

rem Finally the boring bit of checking lots of bloody line intersections

function Sprite_Collision_Check(SA, SB)

`setup variables

SMALL_NUM#=0.00000001

D as float

DU as float

DV as float

SI as float

TI as float

`default negative result

collision_return=0

`firstly check if within collision radius

distance_between_pivots#=SQRT((User_sprite(SA).X-User_sprite(SB).X)^2 + (User_sprite(SA).Y-User_sprite(SB).Y)^2)

if distance_between_pivots#<User_sprite(SA).radius+User_sprite(SB).radius

`hmm this bit could be slow

For a=1 to User_sprite(SA).line_number

For b=1 to User_sprite(SB).line_number

set vector2 Uvector, T_lines(SA,a).X2-T_lines(SA,a).X1, T_lines(SA,a).Y2-T_lines(SA,a).Y1

set vector2 Vvector, T_lines(SB,b).X2-T_lines(SB,b).X1, T_lines(SB,b).Y2-T_lines(SB,b).Y1

set vector2 Wvector, T_lines(SA,a).X1-T_lines(SB,b).X1, T_lines(SA,a).Y1-T_lines(SB,b).Y1

D=perp(Uvector, Vvector)

`test if parallel lines

if abs(D)>SMALL_NUM#

SI=perp(Vvector, Wvector)/D

If SI>0 and SI<1

TI=perp(Uvector, Wvector)/D

If TI>0 and TI<1

collision_return=1

endif

if collision_return=1 then exit

Next b

if collision_return=1 then exit

Next a

endif

endfunction collision_return

rem Calculate the perp product

function perp(VectorA, VectorB)

D as float

D=((x vector2(VectorA) * y vector2(VectorB)) - (y vector2(VectorA) * x vector2(VectorB)))

endfunction D

`*******************************************************************************************

function Transform_collision_coords(number)

cosine_multiple#=cos(-1*sprite angle(number))

sine_multiple#=sin(-1*sprite angle(number))

scale_X#=(sprite scale x(number)/100.0)

scale_Y#=(sprite scale y(number)/100.0)

for l=1 to User_sprite(number).line_number

T_lines(number, l).X1=((lines(number, l).X1*scale_X#)*cosine_multiple#) + ((lines(number, l).Y1*scale_Y#)*sine_multiple#)+User_Sprite(number).X

T_lines(number, l).Y1=(-(lines(number, l).X1*scale_X#)*sine_multiple#) + ((lines(number, l).Y1*scale_Y#)*cosine_multiple#)+User_Sprite(number).Y

T_lines(number, l).X2=((lines(number, l).X2*scale_X#)*cosine_multiple#) + ((lines(number, l).Y2*scale_Y#)*sine_multiple#)+User_Sprite(number).X

T_lines(number, l).Y2=(-(lines(number, l).X2*scale_X#)*sine_multiple#) + ((lines(number, l).Y2*scale_Y#)*cosine_multiple#)+User_Sprite(number).Y

next l

`set the new range check as well

if scale_X#>scale_Y#

max_scale#=scale_X#

else

max_scale#=scale_Y#

endif

User_Sprite(number).Radius=User_Sprite(number).Orig_Radius*max_scale#

endfunction

`*******************************************************************************************

rem Load Sprite Function

function Load_Sprite(Name$, FileType$, number)

`Simple loading and creating sprite

load image "Input/"+Name$+FileType$, number

Sprite number, 0, 0, number

`Open the sprites col file to extract important data

open to read 1, "Output/"+Name$+".col"

read file 1, line_number

read file 1, offset_X

read file 1, offset_Y

read float 1, User_Sprite(number).Orig_Radius

read file 1, User_Sprite(number).Mass

`Read out all the polar coords into the global polar array

For l=1 to line_number

read float 1, lines(number,l).X1

read float 1, lines(number,l).X2

read float 1, lines(number,l).Y1

read float 1, lines(number,l).Y2

next l

`Read out all the normals

For l=1 to line_number

write float 1, normals(number,l).X

write float 1, normals(number,l).Y

next l

`close file

close file 1

`misc clean up

User_sprite(number).line_number=line_number

offset sprite number, offset_X, offset_Y

hide sprite number

endfunction

`*******************************************************************************************

function draw_lines_on(number)

for l=1 to User_sprite(number).line_number

line T_lines(number,l).X1, T_lines(number,l).Y1, T_lines(number,l).X2, T_lines(number,l).Y2

next l

endfunction

`*******************************************************************************************

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Author Name:	haggisman
CodeBase Entries:	2

CodeBase - Nearly pixel perfect sprite collision detection

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DarkBASIC Professional Source Code

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