UnrealScript Game Programming Cookbook

Miscellaneous Recipes

228

We then draw a debug line so that we can see the trace. The line takes our start trace

and end trace as parameters. You don't need this line, but it certainly makes your job

far easier.

5. Let's go over to the next step, that is, converting 3D coordinates into a 2D space.
   /* Projection for the crosshair to convert 3d coords
   into 2d /
   ScreenPos = Canvas.Project(HitLocation);
   /* If we haven't hit any actors... /
   if (HitActor == None )
   {
   HitActor = (HitActor == None)? None
   : Pawn(HitActor.Base);
   HitLocation = EndTrace;
   ScreenPos = Canvas.Project(HitLocation);
   }

ScreenPos, or the 2D vector we want to draw the crosshair on, is using our Canvas.

Project function and takes HitLocation as a parameter. Project is used when

you want to take a 3D coordinate and draw it on a 2D space, like our HUD. The opposite

function, Deproject, takes a 2D coordinate and converts it to 3D space.

Our HitLocation parameter changes depending on how we set that value. Our

HitLocation parameter is the actor our trace has crossed. If we haven't hit any

actors, HitLocation is where the trace ends (that is, it may just extend off into

the distance on a map without walls).

6. Now we need to draw the actual crosshair.
   /* Draws the crosshair for no one - Grey/
   CrosshairSize = 28 (Canvas.ClipY / 768)
   (Canvas.ClipX /1024);
   Canvas.SetDrawColor(100,100,128,255);

// Crosshair in center of trace

Canvas.SetPos(ScreenPos.X - (CrosshairSize * 0.5f),

ScreenPos.Y -(CrosshairSize * 0.5f));

Canvas.DrawTile(class'UTHUD'.default.AltHudTexture,

CrosshairSize, CrosshairSize, 600, 262, 28, 27);

return false;

Our crosshair size uses the edge of our screen, both the X and Y values, then divides

those values by the standard screen resolution (1020 x 768) and multiples it by 28

so that it is large enough to see. Our crosshair color can be anything we'd like, but I've

set it so that it is gray for now.