Starfield Behavior

 

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Creates a 3d starfield you can "fly" through

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---------------------------------------- -- 3D stars behaviour -- Barry Swan, 28/06/2000 -- gerbil@theburrow.co.uk -- http://www.theburrow.co.uk -- All rights reserved ---------------------------------------- property pSN property pX, pY, pZ property pSize property pSpeed property pCenterX, pCenterY property pMaxX, pMaxY property pStarSize, pRandomiseStarSize property pMouseMove, pMouseSpeed property pClipToStage on beginSprite me      -- Store the sprite number for fast access      pSN = me.spriteNum      -- Store center of screen      pCenterX = (the stageRight - the stageLeft) / 2   pCenterY = (the stageBottom - the stageTop) / 2      -- Define clipping boundaries      pMaxX = the stageRight   pMaxY = the stageBottom      -- Create default star size      pSize = pStarSize * 4000      -- Initialise rest of star properties      me.mReset()   pZ = random(1000) + 1000    end on prepareFrame me      -- Mouse movement (if switched on)      if pMouseMove then     tDX = (pCenterX - the mouseH) * pMouseSpeed / pCenterX     tDY = (pCenterY - the mouseV) * pMouseSpeed / pCenterX          -- Move the star          me.mMove(tDX, tDY)   end if      -- Update the star position      pZ = pZ - pSpeed      -- If star is too close then reset      if pZ < 20 then me.mReset()      -- Find screen position of star      tX = (pX * pCenterX / pZ) + pCenterX   tY = (pY * pCenterY / pZ) + pCenterY      -- If star is outside the screen and clipping is switched on then reset      if pClipToStage AND (tX < 0 OR tX > pMaxX OR tY < 0 OR tY > pMaxY) then me.mReset()      -- Find scaling factor for size of star onscreen      tSize = pSize / pZ      -- Draw the star sprite      sprite(pSN).loc = point(tX, tY)   sprite(pSN).width = tSize   sprite(pSN).height = tSize    end on mReset me      -- Create new parameters for star      if pRandomiseStarSize then pSize = random(pStarSize) * 4000      pX = random(3001) - 1501   pY = random(3001) - 1501   pZ = 2000    end on mMove me, tDX, tDY      -- Move star according to specified amount      pX = pX + tDX   pY = pY + tDY    end on getPropertyDescriptionList me      -- Set up the properties      tlData = [:]   tlData[#pSpeed] = [#format: #integer, #default: 10, #range: [#min: 1, #max: 100], #comment: "Star speed (1: slow, 100: fast):"]   tlData[#pStarSize] = [#format: #integer, #default: 5, #range: [#min: 1, #max: 10], #comment: "Star size (1: smallest, 10: largest):"]   tlData[#pRandomiseStarSize] = [#format: #boolean, #default: TRUE, #comment: "Star size is randomised between 1 and value set above:"]   tlData[#pMouseMove] = [#format: #boolean, #default: TRUE, #comment: "Use mouse to steer star direction:"]   tlData[#pMouseSpeed] = [#format: #integer, #default: 20, #range: [#min: 1, #max: 100], #comment: "Mouse affect speed (1: Barely, 100: lots):"]   tlData[#pClipToStage] = [#format: #boolean, #default: TRUE, #comment: "Clip star when outside the stage:"]      return tlData    end on getBehaviorDescription me      -- Return description of behaviour      tText = "[Sprite] 3D stars behaviour." & RETURN & RETURN        tText = tText & "Drop this behaviour on a group of sprites to have them act like a 3D star field." & RETURN   tText = tText & "Switching off clipping to stage will result in much less visible stars overall, but will allow stars to be scrolled off the screen and back on again." & RETURN & RETURN      tText = tText & "Properties -" & RETURN   tText = tText & "pSpeed" & TAB & TAB & TAB & "= Speed of star zooming out of the screen (1: slow, 100: fast)." & RETURN   tText = tText & "pStarSize" & TAB & TAB & TAB & "= Relative star size (1: smallest, 10: largest)." & RETURN   tText = tText & "pRandomiseStarSize" & TAB & "= Whether star size is randomised between 1 and value set for pStarSize" & RETURN   tText = tText & "pMouseMove" & TAB & TAB & "= Whether to use mouse position to steer star direction." & RETURN   tText = tText & "pMouseSpeed" & TAB & TAB & "= How much the mouse steers the star (1: Barely, 100: lots)." & RETURN   tText = tText & "pClipToStage" & TAB & TAB & "= Whether to clip the star when it is outside the stage." & RETURN & RETURN      tText = tText & "Internal handlers -" & RETURN   tText = tText & "mReset()" & TAB & TAB & TAB & "= Resets the star to far away and randomises position and size (according to properties set).." & RETURN   tText = tText & "mMove( tDX, tDY )" & TAB & TAB & "= Moves the star left/right and up/down according to the passed parameters." & RETURN & RETURN      tText = tText & "Written by Barry Swan (gerbil@theburrow.co.uk)."      return tText    end

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