計(jì)算機(jī)圖形學(xué)課件-基本元光柵化

4光柵化：RasterizingobjectsintoPrimitivesarecontinuous;screenisAlgorithmsforefficientgenerationofthesamplescomprisingthisapproximationBresenhamNaive角度DDA問題是什么問題是什么77輸入:起點(diǎn)(x0,y0),終點(diǎn)(xn,問題完整否紅點(diǎn)?問題完整否

88Requirements約Uniformthickness&No9

SimpleMethodkdyynmovefromx0to(x,int

xnSimpleMethodLineSimple(intx0,inty0,intxn,intyn){k=(xn-x0)/(yn-y0);b=y0-kx03次:*,+,for(x=x0;x<=x3次:*,+,{能否改進(jìn)Pixel(x,(int)(y+0.5));能否改進(jìn)}}SimpleMethodmovefromx0to??yiy0i*??y2y02ky1y0k數(shù)值微分法DDAObserve:y+=kateachxstep(k=yi1yiy2y1ky1y0DDALineDDA(intx0,inty0,intxn,intyn){k=(xn-x0)/(yn-y0);b=y0-kx02次:+,for(x=x0;x<=xn2次:+,{能否改進(jìn)Pixel(x,(int)(y+0.5));能否改進(jìn)}}Review問題再思It'slikemarchingaraythroughtheSelectpixelverticallyclosesttoline規(guī)律Review問題再思規(guī)律中點(diǎn)線算法MidpointIfwe'reatpixelP,thenextpixelmustbeeitherPdMidpointHowtodeterminewhichpixeltochoose:PdorChoosePdifsegmentpassesbelowmiddlepointChoosePuifsegmentpassesaboveHowtoexpress“segmentpassesaboveM”?其它判別方法BresenhamBresenham's回到Midpoint直線方程F(x,y)= 上方 下一步Midpointi1

F(Mi1)F(Mi)F(xi2,

)F(xi1,

條件F(xi2,yi0.5)F(xi1,yi條件 F(x2,y1.5)F(x a,iab, 0F(x01,y00.5)aMidpointLineMidpoint(intx0,inty0,intxn,intyn){a=y0-yn;b=xn-x繼續(xù)改進(jìn)繼續(xù)改進(jìn){if(d<0){x++;y++;d=d+d1;}else{x++;d=d+d2;}} Circle圓光柵CircleNaive角度DDA Circley=-y=-y y + =yY=Sqrt(R2- 角度DDAx=x0+Rcosy=y0+Rsindx=-Rsinddy=Rcosdxn+1=xn+dxyn+1=yn+ xn+1=xn+dx=xn-Rsind=xn-(yn-y0)dyn+1=yn+dy=yn+Rcosd=yn+(xn-x0顯然，確定x,y的初值及d值后，即可以增量方式獲得圓周上的坐標(biāo)，然后取整可得象素坐標(biāo)。但要采用浮點(diǎn)運(yùn)算、乘法運(yùn)算、取整運(yùn)算。 利用圓的對(duì)稱性，只須討論1/8P（Xp，Yp

圓弧

高像— — 像

素中低像P為當(dāng)前點(diǎn)亮象素，那么，下一個(gè)點(diǎn)亮的象素可能是（Xp+1，Yp）或P2（Xp+1，Yp+1) +Y2-R2；F（X，Y）=