Fast Image Scaling

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mike_g	Created : 20 August 2007 Edited : 20 August 2007 Language : Blitz Fast Image Scaling
This is some code I am working on for my raycaster. It creates an array of scaled images to remove the need for realtime scaling. Each frame has its own handle and is sized appropriately to save RAM usage. At them moment there is only 1 scaled image array, but I intend to move that into a type so there can be as many as needed in-game. Anyway heres a test image for it: And heres the code: AppTitle "Fast Image Scaling" Graphics 640, 480, 32, 2 SetBuffer BackBuffer() ;Each image has an array of handles for scaled versions ;The more handles the greater the scale detail Const SCALE_DETAIL = 50 ;50 frames Const SCALE_RANGE = 2 ;between 2 and 0.1 image = LoadImage("tree.png") Dim scaled_image(SCALE_DETAIL) Scale(image) FreeImage(image) ;---------------------------------------------------------------------------------------------------; ;****************************** DEMO PROGRAM *************************************************; ;---------------------------------------------------------------------------------------------------; SeedRnd MilliSecs() ;FRAME RATE VARIABLES Global old_time = MilliSecs() Global frame_count, fps Type tree Field image Field scale Field x, y End Type InitTrees() inc=1: i=5 While Not KeyHit(1) Cls DrawTrees() KeyInput() FPS() Flip 0 Wend ClearScaled() ;free scaled images ;---------------------------------------------------------------------------------------------------; ;**************************** SCALE FUNCTIONS ***********************************************; ;---------------------------------------------------------------------------------------------------; Function Scale(image) Local src_x, src_y ;co-ords to read from original image Local src_w, src_h ;width and height of original Local dst_x, dst_y ;co-ords to draw to scaled image Local dst_w, dst_h ;width and height of scaled image Local col, inc# ;colour to draw , scale size increment src_w = ImageWidth(image) src_h = ImageHeight(image) inc# = Float(SCALE_RANGE) / Float(SCALE_DETAIL) SetBuffer ImageBuffer(image, mask) For i = 1 To SCALE_DETAIL image_size# = image_size# + inc# dst_w = Floor(src_w image_size#) dst_h = Floor(src_h * image_size#) scaled_image(i) = CreateImage(dst_w, dst_h) LockBuffer ImageBuffer(image) LockBuffer ImageBuffer(scaled_image(i)) For dst_y=0 To dst_h src_y = Floor(dst_y / image_size#) For dst_x=0 To dst_w src_x = Floor(dst_x / image_size) col = ReadPixelFast(src_x, src_y) WritePixelFast(dst_x, dst_y, col, ImageBuffer(scaled_image(i))) Next Next UnlockBuffer ImageBuffer(image) UnlockBuffer ImageBuffer(scaled_image(i)) MaskImage scaled_image(i), 255, 0, 255 Next SetBuffer BackBuffer() End Function Function ClearScaled() For i = 1 To SCALE_DETAIL FreeImage(scaled_image(i)) Next End Function ;---------------------------------------------------------------------------------------------------; ;****************************** DEMO FUNCTIONS *************************************************; ;---------------------------------------------------------------------------------------------------; Function KeyInput() If KeyDown(200) ResizeTrees(1) Else If KeyDown(208) ResizeTrees(-1) EndIf End Function Function ResizeTrees(inc) For t.tree = Each tree go=0 If t\scale < SCALE_DETAIL And t\scale > 1 Then go =1 t\scale = t\scale +inc If go = 1 t\image = scaled_image(t\scale) t\y = 240-(ImageHeight(t\image)/2) EndIf Next End Function Function DrawTrees() For t.tree = Each tree DrawImage t\image, t\x, t\y Next End Function Function InitTrees() ;Make trees For i = 1 To 10 t.tree = New tree t\scale = Rand(1, SCALE_DETAIL) t\image = scaled_image(t\scale) t\x = Rand(0, 600) t\y = 240-(ImageHeight(t\image)/2) Next ;Sort trees by distance a.tree = First tree flag = True While flag flag = False b.tree = Last tree While a <> b c.tree = Before b If c = Null Then Exit If b\scale < c\scale Insert c After b flag=True Else b=c EndIf Wend a = After b Wend End Function Function FPS() If MilliSecs() > old_time+1000 old_time = MilliSecs() fps=frame_count frame_count=0 EndIf Color 255, 255, 255 Text 0, 0, "FPS: "+fps frame_count=frame_count+1 End Function --v \|edit\| Oh yeah and press up/down to zoom in/out. \|edit\|

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Friday, 24 August 2007, 22:22
Evil Roy Ferguso	Question: since this appears to pre-calculate the scaled images, is there any particular reason you have chosen not to use the built-in commands for this purpose? Function Scale(image) Local tmp Local inc# ; eliminate the fuzz / handsome magenta border caused by Blitz's misguided bilinear filtering. TFormFilter False inc = Float(SCALE_RANGE) / Float(SCALE_DETAIL) For i = 1 To SCALE_DETAIL scaled_image(i) = CopyImage(image) ScaleImage scaled_image(i), incFloat(i), incFloat(i) Next End Function --v Besides that, though, your code causes a memory access violation. I do have tree.png in the appropriate directory, and the above code works -- although you need to MaskImage the original tree image, CopyImage will transfer the mask to the scaled images as well.
Saturday, 25 August 2007, 05:22
mike_g	Question: since this appears to pre-calculate the scaled images, is there any particular reason you have chosen not to use the built-in commands for this purpose? Oh, yeah I guess I went about this the hard way o_0 I started out coding this in realtime tho, then changed to doing it all pre-drawn. Besides that, though, your code causes a memory access violation. I do have tree.png in the appropriate directory, and the above code works Thats strange. It works fine for me. Did you get where the MAV was? It could be the Read/Write pixel fasts. Anyways, I had done a little more work to this. The code below sets up a type for each image, so you can use as many different images as you want. I removed the fast bit from the read/write pixels. Hopefully I should work now. If you or anyone else is still getting MAVs, let us know. Cheers. SeedRnd MilliSecs() ;FRAME RATE VARIABLES Global old_time = MilliSecs() Global frame_count, fps Type tree Field image Field scale Field x, y End Type InitTrees() inc=1: i=5 While Not KeyHit(1) Cls DrawTrees() KeyInput() FPS() Flip Wend ClearScaled() ;free scaled images ;---------------------------------------------------------------------------------------------------; ;****************************** SCALE FUNCTIONS ***********************************************; ;---------------------------------------------------------------------------------------------------; Function CreateScaledImage(image, name$) im.image = New image im\name = "tree" Local src_x, src_y ;co-ords to read from original image Local src_w, src_h ;width and height of original Local dst_x, dst_y ;co-ords to draw to scaled image Local dst_w, dst_h ;width and height of scaled image Local col, inc# ;colour to draw , scale size increment src_w = ImageWidth(image) src_h = ImageHeight(image) inc# = Float(SCALE_RANGE) / Float(SCALE_DETAIL) SetBuffer ImageBuffer(image, mask) For i = 1 To SCALE_DETAIL image_size# = image_size# + inc# dst_w = Floor(src_w image_size#) dst_h = Floor(src_h * image_size#) im\frames[i] = CreateImage(dst_w, dst_h) LockBuffer ImageBuffer(image) LockBuffer ImageBuffer(im\frames[i]) For dst_y=0 To dst_h src_y = Floor(dst_y / image_size#) For dst_x=0 To dst_w src_x = Floor(dst_x / image_size) col = ReadPixel(src_x, src_y) WritePixel(dst_x, dst_y, col, ImageBuffer(im\frames[i])) Next Next UnlockBuffer ImageBuffer(image) UnlockBuffer ImageBuffer(im\frames[i]) MaskImage im\frames[i], 255, 0, 255 Next SetBuffer BackBuffer() End Function Function ClearScaled() For im.image = Each image For i = 1 To SCALE_DETAIL FreeImage(im\frames[i]) Next Next End Function ;---------------------------------------------------------------------------------------------------; ;****************************** DEMO FUNCTIONS *************************************************; ;---------------------------------------------------------------------------------------------------; Function KeyInput() If KeyDown(200) ResizeTrees(1) Else If KeyDown(208) ResizeTrees(-1) EndIf End Function Function ResizeTrees(inc) im.image = First image For t.tree = Each tree go=0 If t\scale < SCALE_DETAIL And t\scale > 1 Then go =1 t\scale = t\scale +inc If go = 1 t\image = im\frames[t\scale] t\y = 240-(ImageHeight(t\image)/2) EndIf Next End Function Function DrawTrees() For t.tree = Each tree DrawImage t\image, t\x, t\y Next End Function Function InitTrees() ;Make trees im.image = First image For i = 1 To 100 t.tree = New tree t\scale = Rand(1, SCALE_DETAIL) t\image = im\frames[t\scale] t\x = Rand(0, 600) t\y = 240-(ImageHeight(t\image)/2) Next ;Sort trees by distance a.tree = First tree flag = True While flag flag = False b.tree = Last tree While a <> b c.tree = Before b If c = Null Then Exit If b\scale < c\scale Insert c After b flag=True Else b=c EndIf Wend a = After b Wend End Function Function FPS() If MilliSecs() > old_time+1000 old_time = MilliSecs() fps=frame_count frame_count=0 EndIf Color 255, 255, 255 Text 0, 0, "FPS: "+fps frame_count=frame_count+1 End Function --v

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