image rotation? - BlitzCoder.net

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Socoder -> C/C++/C#/Other -> image rotation?
Sun, 08 Apr 2018, 02:47
spinal	image rotation? I'm working on a little but of code to rotate an image in real time. I'm currently doing it a slow way - for(int y=0; y<height; y++){ for(int x=0; x<width; x++){ int x1 = (x-halfWidth)TIMES; // multiply to avoid using floats int y1 = (y-halfHeight)TIMES; int ux = (x1 * COS - y1 * SIN + HALFTIMES) / TIMES2; // undo above multiplications to get x,y pixels int uy = (x1 * SIN + y1 * COS + HALFTIMES) / TIMES2; if(ux>-halfWidth && ux <halfWidth && uy >-halfHeight && uy <halfHeight){ // grab pixel from 4bbp bitmap uint16_t i = (uy+halfHeight)*(width>>1) + (width-(ux+halfWidth)>>1); uint8_t pixel = image1[i+2]; if (ux&1) col = pixel & 0x0F; else col = pixel>>4; mygame.display.drawPixel(x,y,col); } } } --v However, apparently it's much faster to shear+skew the image and only calculate the angle once per render instead of once per pixel... But I can't get my head around it. Has anyone doe this before? www.drdobbs.com/architecture-and-design/fast-bitmap-rotation-and-scaling/184416337 -=-=- Check out my excellent homepage!
Sun, 08 Apr 2018, 03:36
Jayenkai	Yeah, code-based rotation's never been a good thing. If you have the memory, pre-rotate your sprites whilst loading, to (360/(16 or 32)) degree rotations, and use those.. It's not perfect, but it's better than nothing. I've never attempted to rotate using skews, and although it sounds like it might work, I imagine the fake-rotate might look a little warped by the end of it. But then, given the small resolution, you'll probably be able to get away with it..? -=-=- ''Load, Next List!''
Sun, 08 Apr 2018, 04:15
spinal	Yeah, no RAM, slow processor etc.
Thu, 12 Apr 2018, 09:50
spinal	OK, apparently this is supposed to be really fast as it removes almost all of the math from inside the double loop... link However, the output is completely wonky and wrong, perhaps the sin/cos bit is incorrect? blitz... Graphics 1024,768,0,2 src_width = 640 src_height = 480 angle = 25 sin_angle# = Sin(angle) cos_angle# = Cos(angle) midX = src_width/2 midY = src_height/2 temp_img = LoadImage("d:\psp.bmp") ; 640x480 bmp For j = 0 To src_height deltaY# = j+ 0.5 - midY deltaX# = 0.5 - midX x_computation# = midX + deltaX * cos_angle + deltaY * sin_angle y_computation# = midY - deltaX * sin_angle + deltaY * cos_angle For i = 0 To src_width rotX = x_computation rotY = y_computation If rotX >=0 And rotX < src_width And rotY >=0 And rotY < src_height Then SetBuffer ImageBuffer(temp_img) GetColor i,j SetBuffer FrontBuffer() Plot rotX,rotY End If x_computation = x_computation + cos_angle# y_computation = y_computation + sin_angle# Next Next While Not KeyHit(1) Wend End --v -=-=- Check out my excellent homepage!
Thu, 12 Apr 2018, 11:02
Jayenkai	jscrw#=1024 jscrh#=768 Graphics jscrw,jscrh,0,2 SetBuffer BackBuffer() temp_img = LoadImage("netblitz3d.PNG") ; 640x480 bmp src_width = ImageWidth(temp_img) src_height = ImageHeight(temp_img) angle = 45 midX = (jscrw/2) midY = (jscrh/2) j#=0 i#=0 Repeat OffsetXX#=Sin(angle) OffsetXY#=-Cos(angle) OffsetYX#=Sin(angle+90) OffsetYY#=-Cos(angle+90) LockBuffer ImageBuffer(temp_img) For j = 0 To src_height-1 deltaY# = (j+ 0.5) - midY deltaX# = 0.5 - midX x_computation# = midX - ( (offsetXX(src_width0.5)) + (offsetYX(src_height0.5)) ) + (jOffsetYX) y_computation# = midY - ( (offsetXY(src_width0.5)) + (offsetYY(src_height0.5)) ) + (jOffsetYY) For i = 0 To src_width-1 rotX = x_computation rotY = y_computation If rotX >=0 And rotX < jscrw And rotY >=0 And rotY < jscrh Then argb=ReadPixelFast(i,j,ImageBuffer(temp_img)) Color 0,0,argb Plot rotX,rotY End If x_computation = x_computation + OffsetXX# y_computation = y_computation + OffsetXY# Next If (j Mod 10)=0 Then Flip False If KeyHit(1) Then End Next UnlockBuffer ImageBuffer(temp_img) angle=angle+15 Until KeyHit(1) End --v I smudged together the code you posted, along with my tilemap rotation code from the other day. Seems nice and fast, I think.. -=-=- ''Load, Next List!''
Thu, 12 Apr 2018, 14:00
spinal	Right, I won't claim to follow the math 100%, or even 70% but this is apparently the 'correct' way... We assume that because were drawing a straight line on the screen, then the line we are copying from our source image is also straight. We then create a vector based on the angle we are rotating to outside of the loops so that it is done only once per render, then its a case of additions on the x and y going from that vector. Graphics 800,600,0,2 temp_img = LoadImage("d:\psp.bmp") ; 640x480 bmp dstW = 800 dstH = 600 srcW = ImageWidth(temp_img) srcH = ImageHeight(temp_img) fDstCX = dstW/2 fDstCY = dstH/2 fSrcCX = srcW/2 fSrcCY = srcH/2 fAngle = 15 fScale# = .5 For fAngle = 0 To 359 duCol# = Sin(-fAngle) * (1.0 / fScale); * times dvCol# = Cos(-fAngle) * (1.0 / fScale); * times duRow# = dvCol dvRow# = -duCol startingu# = fSrcCX - (fDstCX * dvCol + fDstCY * duCol) startingv# = fSrcCY - (fDstCX * dvRow + fDstCY * duRow) rowu# = startingu rowv# = startingv For y = 0 To dstH u# = rowu v# = rowv For x = 0 To dstW If u >=0 And u < srcW And v >=0 And v < srcH Then SetBuffer ImageBuffer(temp_img) GetColor u,v SetBuffer FrontBuffer() Plot x,y Else Color 0,0,0 Plot x,y End If u = u + duRow v = v + dvRow Next rowu = rowu + duCol rowv = rowv + dvCol If KeyHit(1) Then End Next Next While Not KeyHit(1) Wend End --v There's a lot of floats there, which slow everything down a lot, also its in basic, which is also slow Just got to figure how to fixed-point the whole thing... -=-=- Check out my excellent homepage!