TheGameCreators - CodeBase - Mouse picking [DBC][memblocks]

Return to the CodeBase listing

Category: 3D Maths

Version: 1.0

Information

Uploaded: 5th Apr 2004 10:45

Modified: 5th Apr 2004 10:49

Author: Arkheii

Summary

Polygon-perfect mouse picking example.

Full Description

DarkBASIC Source Code

` This code was downloaded from The Game Creators

` It is reproduced here with full permission

` http://www.thegamecreators.com

`Polygon mouse picking example by r_kabouter

`This code is very inefficient, but shows

`how this can be done without that raycasting

`and dot product crap. Optimize this in any

`way you wish. I recommend you do that anyway.

`If this helps you, please direct any credits to

`Yin Nadie, who wrote a tutorial over at

`http://www.ilogicgames.com because the

`equations here were found at his tutorial. It

`may also be good if you tell Yin that he was

`very helpful to you by e-mailing him at

`yin_nadie@hotmail.com

`Yin's tutorial was actually about collision,

`but I thought it could also be used to solve

`the mouse pick problem that everyone seems to

`have. So far this only works with objects and

`models, not matrices etc., but it's a start.

`Basically this works by taking a face and

`using it to make an imaginary triangle on

`the screen and test if the mouse is in that

`imaginary triangle.

set display mode 800,600,16

sync on

sync rate 0

autocam off

backdrop on

color backdrop 0

hide mouse

`Prepare a few objects: test1 is a cylinder, test2 is a cone.

`For this I made a few functions so I don't have to remember

`the object numbers. The functions are somewhere in the

`bottom of the code.

`Note that you can replace these with models that you want

`to load. You have to modify the code on your own though.

`I'd love to include my entire object loading library,

`but... naaah.

test1=makecylinder(4.0)

test2=makecone(4.0)

position object test1,-4,0,0

position object test2,4,0,0

`Dimmed an array of 3 elements. This is for the invisible

`plains that will be used to get the screen positions of

`vertices later. Since each face has 3 vertices, we have

`3 separate objects for each one of them. The makeplain()

`function is like the makecylinder() and makecone() functions

`earlier. For this I decided to use a plain since they take

`up less memory, having only 3 vertices and whatnot. They

`are also hidden because we don't have to see them.

`*****Make sure that you copy the following block of code

`in your program! These are needed for the function later.

`You may modify it so that it uses the standard

`make object plain command if you do not want to use the

`makeplain() function I added. Unless you want to dig

`into the function later and change variable names, I

`suggest that you stick to the array name pointerobj.*****

dim pointerobj(3)

for i=0 to 2

pointerobj(i)=makeplain(1.0,1.0)

hide object pointerobj(i)

next i

`Position the camera somewhere exciting :D

position camera 0,16,-16

point camera 0,0,0

`Beginning of the main loop.

`Duh.

ink rgb(255,255,255),0

set cursor 1,1

print screen fps()

`Just to show that the mouse pick function isn't a screen

`distance cheat, I rotate and move the objects. The float

`rot1# is the rotation value for the object test1, the

`cylinder. test1x# and test1z# are the x and z positions

`for the cylinder. rot2#, test2x#, and test2z# are the

`same as the previous 3 variables, except that they are

`the ones to be used by the test2 object, the cone.

rot1#=wrapvalue(rot1#+0.5)

rot2#=wrapvalue(rot2#-0.5)

`How convenient. We can use the rot variables in the sin

`and cos functions to make the objects move in circular

`directions.

test1x#=sin(rot1#)*4.0

test1z#=cos(rot1#)*4.0

test2x#=sin(rot2#)*8.0

test2z#=cos(rot2#)*8.0

rotate object test1,rot1#,rot1#,rot1#

rotate object test2,rot2#,rot2#,rot2#

position object test1,test1x#,0,test1z#

position object test2,test2x#,0,test2z#

`Replace the mouse image with something more precise.

dot mousex(),mousey()

circle mousex(),mousey(),4

`Just a simple mouse handler so that the mouse is only

`pressed once instead of being held down. Convenient for

`a big performance later on. If the mouse click is valid,

`the variable mouse is set to 1, which will be used later.

if mouseclick()

if oldmouse=0

mouse=1

oldmouse=1

else

mouse=0

endif

else

oldmouse=0

mouse=0

endif

`mouse=1, which means that a valid mouseclick was detected.

`Here it uses clickobject(objectNumber) to test if the

`mouse was on top of an object when the mouse was pressed.

`Notice that this will have to check for *all* the objects

`in the scene. In other words, it's not optimized. That's the

`problem you have to take care of on your own.

`If clickobject() says that the mouse was in fact on top of

`an object when the mouse was clicked, it returns a 1, else

`it returns a 0. For convenience, instead of using multiple

`if statements, I immediately assign the return values to

`the variables testXselected so we can re-check them again

`later.

`Also note that I used the mouse handler for this. If

`I didn't use the mouse handler and the mouse button was held

`down, it would keep checking the objects if the mouse is

`above them, which would result in terrible performance

`problems.

if mouse=1

test1selected=clickobject(test1)

test2selected=clickobject(test2)

endif

`This checks if both objects were selected. Remember that

`this code is unoptimized, so this is very unreliable when

`you have many objects on the scene(especially if they have

`lots of polys). What this does is check which object is

`closer to the camera during the instance of having 2 objects

`under the mouse. Using an estimated distance equation (meaning

`without the square root), we can check if which object is closer

`to the camera. That way, the farther object is deselected so

`that only one object is selected at a time.

if test1selected=1 and test2selected=1

test1dist#=object position x(test1)^2+object position y(test1)^2+object position z(test1)^2

test2dist#=object position x(test2)^2+object position y(test2)^2+object position z(test2)^2

if test1dist#<test2dist#

test2selected=0

endif

if test2dist#<test1dist#

test1selected=0

endif

`Here's what we do about selected objects. If the object

`is selected then color it red, else color it white.

`Easy.

if test1selected=1

color object test1,rgb(255,0,0)

else

color object test1,rgb(255,255,255)

endif

if test2selected=1

color object test2,rgb(255,0,0)

else

color object test2,rgb(255,255,255)

endif

`End of the loop.

sync

loop

`*****FUNCTIONS*****

function makecone(value#)

ctr=0

true=1

while ctr <= 65535 and true <> 0

inc ctr

if object exist(ctr)=0

true=0

make object cone ctr,value#

endif

endwhile

endfunction ctr

function makecylinder(value#)

ctr=0

true=1

while ctr <= 65535 and true <> 0

inc ctr

if object exist(ctr)=0

true=0

make object cylinder ctr,value#

endif

endwhile

endfunction ctr

function makeplain(width#,height#)

ctr=0

true=1

while ctr <= 65535 and true <> 0

inc ctr

if object exist(ctr)=0

true=0

make object plain ctr,width#,height#

endif

endwhile

endfunction ctr

`I found the equations for this at www.ilogicgames.com

`I don't know how it works, and neither does the source,

`but that doesn't matter. Basically, we take 3 points on

`the screen to define a triangle on the screen. That's an

`x and y value for each vertex of the triangle, thus the

`first 6 variables we pass to the function. The last 2 are

`the mouse positions. If the mouse coords are within the

`2D triangle defined by our 3 vertices, it returns a 1.

`This will be used later in the clickobject() function.

`2D vertices are obtained by using the object screen x(),

`y() and z() functions so that 3D polygons can also be

`checked.

function plaincontain(xa#,ya#,xb#,yb#,xc#,yc#,x,y)

x#=x

y#=y

x1#=xb#-xa#

x2#=xc#-xa#

x3#=x#-xa#

y1#=yb#-ya#

y2#=yc#-ya#

y3#=y#-ya#

a# = ( x1# * y2# ) - ( x2# * y1# )

b# = ( x1# * y3# ) - ( x3# * y1# )

c# = ( x2# * y3# ) - ( x3# * y2# )

if ( a# * b# ) > 0 and ( a# * c# ) < 0 and ( a# * ( a# + c# - b# ) ) > 0

collide=1

else

collide=0

endif

endfunction collide

`The workhorse that takes up so much memory and cpu.

`Since we cannot obtain vertex data, I had to use

`memblocks. Make sure that you do not use mesh 1

`and memblock 1 because those are used by this function.

`This loads up the object specified by objnum as a mesh

`so it can be converted to a memblock. It then checks

`the faces and verts there. After it's all done, it

`deletes the mesh and the memblock. Not very efficient,

`but remember that this is DBC, hehe.

`To make it a bit quicker, it stops checking as soon

`as any polygon was detected to be under the mouse,

`that way it doesn't waste valuable cpu time checking

`faces when it already knows that the object is already

`under the mouse.

function clickobject(objnum)

selected=0

make mesh from object 1,objnum

make memblock from mesh 1,1

vertoffset=memblock dword(1,4)

numface=memblock dword(1,16)

faceoffset=memblock dword(1,20)

for face=0 to numface-1

vertindexa=memblock dword(1,faceoffset+(face*28)+4)

vertindexb=memblock dword(1,faceoffset+(face*28)+12)

vertindexc=memblock dword(1,faceoffset+(face*28)+20)

ax#=memblock float(1,vertoffset+(vertindexa*12))

ay#=memblock float(1,vertoffset+(vertindexa*12)+4)

az#=memblock float(1,vertoffset+(vertindexa*12)+8)

bx#=memblock float(1,vertoffset+(vertindexb*12))

by#=memblock float(1,vertoffset+(vertindexb*12)+4)

bz#=memblock float(1,vertoffset+(vertindexb*12)+8)

cx#=memblock float(1,vertoffset+(vertindexc*12))

cy#=memblock float(1,vertoffset+(vertindexc*12)+4)

cz#=memblock float(1,vertoffset+(vertindexc*12)+8)

position object pointerobj(0),ax#,ay#,az#

position object pointerobj(1),bx#,by#,bz#

position object pointerobj(2),cx#,cy#,cz#

asx#=object screen x(pointerobj(0))

asy#=object screen y(pointerobj(0))

bsx#=object screen x(pointerobj(1))

bsy#=object screen y(pointerobj(1))

csx#=object screen x(pointerobj(2))

csy#=object screen y(pointerobj(2))

if plaincontain(asx#,asy#,bsx#,bsy#,csx#,csy#,mousex(),mousey())

selected=1

exit

endif

next face

delete mesh 1

delete memblock 1

endfunction selected

Download

Please login to download

Comments

No comments yet.

Author Name:	Arkheii
CodeBase Entries:	4

CodeBase - Mouse picking [DBC][memblocks]

Information

Summary

Full Description

DarkBASIC Source Code

Download

Screen Shot

Author

Comments