算法填充三角形 [英] Algorithm to fill triangle
问题描述
我使用下面的代码：
void triangle（int xa， int ya，int xb，int yb，int xc，int yc，TGAImage& image，TGAColor color）
{
line（xa，ya，xb，yb，image，color）;
line（xa，ya，xc，yc，image，color）;
line（xb，yb，xc，yc，image，color）;
for（int x = xa; x <= xb; x ++）
{
for（int y = ya; y <= yb; y ++）
{
line（xc，yc，x，y，image，white）;
$ b $ / code> 使用三角形（100,100,100,400,400,100，图像，红色）; 它正常工作。
但是，如果我将X（xa，ya）和Z（xc，yc）的坐标交换为不能填充我的方形。
使用三角形（70，50，200，100，20，150，图片，红色）; 绘制三角形，但填充出界
解决方案
lang-cpp prettyprint-override> // ---------------------------------- -----------------------------------------
class gfx_main
{
public：
Graphics :: TBitmap * bmp;
int ** pyx，xs，ys;
gfx_main（）;
〜gfx_main（）;
void resize（int _xs = -1，int _ys = -1）;
void troj（int x0，int y0，int x1，int y1，int x2，int y2，int col）; //这是填充三角形
void _troj_line（int * pl，int * pr，int x0，int y0，int x1，int y1）; //这只是子程序
};
// -------------------------------------------- -------------------------------
gfx_main :: gfx_main（）
{
bmp = new Graphics :: TBitmap;
pyx = NULL;
调整大小（1,1）;
}
// --------------------------------------- ------------------------------------
gfx_main ::〜gfx_main（）
{
delete bmp;
if（pyx）delete [] pyx;
}
// --------------------------------------- ------------------------------------
void gfx_main :: resize（int _xs，int _ys）
{
if（pyx）delete [] pyx; （（_xs> 0）&&（_ ys> 0））{bmp-> Width = _xs; BMP->身高= _ys; }
xs = bmp->宽度;
ys = bmp->高度;
bmp-> HandleType = bmDIB;
bmp-> PixelFormat = pf32bit;
pyx = new int * [ys]; （int y = 0; y< ys; y ++）pyx [y] =（int *）bmp-> ScanLine [y];
}
// --------------------------------------- ------------------------------------
// ---光栅化：--- -------------------------------------------------- -
// ------------------------------------------ ---------------------------------
void gfx_main :: _ troj_line（int * pl，int * pr ，int x0，int y0，int x1，int y1）
{
int * pp;
int x，y，kx，ky，dx，dy，k，m，p;
// DDA变量（d）abs delta，（k）步进方向
kx = 0; DX = X1-X0;如果（dx> 0）kx = + 1;如果（dx< 0）{kx = -1; DX = -dx; }
ky = 0; DY = Y1-Y0;如果（dy> 0）ky = + 1;如果（dy <0）{ky = -1; DY = -dy; }
//根据ky方向的目标缓冲区
if（ky> 0）pp = pl; else pp = pr;
//整数DDA线起点
x = x0; Y = Y0;
//修正端点只是为了确定（错误的除法常量+/- 1会导致最后一点丢失）
pp [y1] = x1;第[Y0] = X0;
if（dx> = dy）// x轴为主
{
k = dy + dy;
m =（dy-dx）; M + =米;
p = m; $（b; b）为（;;）
{
pp [y] = x;
if（x == x1）break;
x + = kx;
if（p> 0）{y + = ky; P + =米; } else p + = k;
}
}
else {// y轴是主
k = dx + dx;
m =（dx-dy）; M + =米;
p = m; $（b; b）为（;;）
{
pp [y] = x;
if（y == y1）break;
y + = ky;
if（p> 0）{x + = kx; P + =米; } else p + = k;
}
}
}
// ----------------------------- ----------------------------------------------
int rgb2bgr（int col）
{
union
{
BYTE db [4];
int dd;
} c;
BYTE q;
c.dd = col;
q = c.db [0]; c.db [0] = c.db [2]; c.db [2] = Q;
返回c.dd;
}
// --------------------------------------- ------------------------------------
void gfx_main :: troj（int x0，int y0，int x1，int y1，int x2，int y2，int col）
{
col = rgb2bgr（col）;
int * pl，* pr; //左/右缓冲区
pl = new int [ys];
pr = new int [ys];
int x，y，yy0，yy1，xx0，xx1;
//边界线坐标到缓冲区
_troj_line（pl，pr，x0，y0，x1，y1）;
_troj_line（pl，pr，x1，y1，x2，y2）;
_troj_line（pl，pr，x2，y2，x0，y0）;
// y范围
yy0 = y0;如果（yy0> y1）yy0 = y1;如果（yy0> y2）yy0 = y2;
yy1 = y0; if（yy1
for（y = yy0; y <= yy1; y ++）
{
if（pl [y]
for（x = xx0; x <= xx1; x ++）
pyx [y] [x] = col;
}
delete [] pl;
delete [] pr;
}
// --------------------------------------- ------------------------------------
示例用法：
$ b
/ / init
gfx_main gfx;
gfx.resize（640,480）;
//清除屏幕
TCanvas * scr = gfx.bmp->画布;
scr-> Pen - > Color = clAqua;
scr->字体 - >颜色= clYellow;
scr-> Brush-> Color = clBlack;
scr-> FillRect（TRect（0,0，xs，ys））;
//三角形
troj（10,10,120,60,70,100，clAqua）;
//这里gfx.bmp包含渲染的图像...
来源基于这：
i'm thinking about rasterization triangle algorithm. ( triangle_rasterization_lesson )
I wtote the following code:
void triangle(int xa, int ya, int xb, int yb, int xc, int yc, TGAImage &image, TGAColor color)
{
line(xa, ya, xb, yb, image, color);
line(xa, ya, xc, yc, image, color);
line(xb, yb, xc, yc, image, color);
for (int x = xa; x<=xb; x++)
{
for (int y = ya; y<=yb; y++)
{
line(xc, yc, x, y, image, white);
}
}
}
With triangle(100, 100, 100, 400, 400, 100, image, red); it works properly.
But if i swap X(xa, ya) and Z(xc, yc) coordinates to doesn't fill my square.
With triangle(70, 50, 200, 100, 20, 150, image, red); it draws triangle, but filling comes out of bounds.
Where is the problem?
if it helps a bit here is my ancient C++ source for triangle in VCL/GDI:
//---------------------------------------------------------------------------
class gfx_main
{
public:
Graphics::TBitmap *bmp;
int **pyx,xs,ys;
gfx_main();
~gfx_main();
void resize(int _xs=-1,int _ys=-1);
void troj(int x0,int y0,int x1,int y1,int x2,int y2,int col); // this is filled triangle
void _troj_line(int *pl,int *pr,int x0,int y0,int x1,int y1); // this is just subroutine
};
//---------------------------------------------------------------------------
gfx_main::gfx_main()
{
bmp=new Graphics::TBitmap;
pyx=NULL;
resize(1,1);
}
//---------------------------------------------------------------------------
gfx_main::~gfx_main()
{
delete bmp;
if (pyx) delete[] pyx;
}
//---------------------------------------------------------------------------
void gfx_main::resize(int _xs,int _ys)
{
if (pyx) delete[] pyx;
if ((_xs>0)&&(_ys>0)) { bmp->Width=_xs; bmp->Height=_ys; }
xs=bmp->Width;
ys=bmp->Height;
bmp->HandleType=bmDIB;
bmp->PixelFormat=pf32bit;
pyx=new int*[ys];
for (int y=0;y<ys;y++) pyx[y]=(int*)bmp->ScanLine[y];
}
//---------------------------------------------------------------------------
//--- rasterisations: -------------------------------------------------------
//---------------------------------------------------------------------------
void gfx_main::_troj_line(int *pl,int *pr,int x0,int y0,int x1,int y1)
{
int *pp;
int x,y,kx,ky,dx,dy,k,m,p;
// DDA variables (d)abs delta,(k)step direction
kx=0; dx=x1-x0; if (dx>0) kx=+1; if (dx<0) { kx=-1; dx=-dx; }
ky=0; dy=y1-y0; if (dy>0) ky=+1; if (dy<0) { ky=-1; dy=-dy; }
// target buffer according to ky direction
if (ky>0) pp=pl; else pp=pr;
// integer DDA line start point
x=x0; y=y0;
// fix endpoints just to be sure (wrong division constants by +/-1 can cause that last point is missing)
pp[y1]=x1; pp[y0]=x0;
if (dx>=dy) // x axis is major
{
k=dy+dy;
m=(dy-dx); m+=m;
p=m;
for (;;)
{
pp[y]=x;
if (x==x1) break;
x+=kx;
if (p>0) { y+=ky; p+=m; } else p+=k;
}
}
else{ // y axis is major
k=dx+dx;
m=(dx-dy); m+=m;
p=m;
for (;;)
{
pp[y]=x;
if (y==y1) break;
y+=ky;
if (p>0) { x+=kx; p+=m; } else p+=k;
}
}
}
//---------------------------------------------------------------------------
int rgb2bgr(int col)
{
union
{
BYTE db[4];
int dd;
} c;
BYTE q;
c.dd=col;
q=c.db[0]; c.db[0]=c.db[2]; c.db[2]=q;
return c.dd;
}
//---------------------------------------------------------------------------
void gfx_main::troj(int x0,int y0,int x1,int y1,int x2,int y2,int col)
{
col=rgb2bgr(col);
int *pl,*pr; // left/right buffers
pl=new int[ys];
pr=new int[ys];
int x,y,yy0,yy1,xx0,xx1;
// boundary line coordinates to buffers
_troj_line(pl,pr,x0,y0,x1,y1);
_troj_line(pl,pr,x1,y1,x2,y2);
_troj_line(pl,pr,x2,y2,x0,y0);
// y range
yy0=y0; if (yy0>y1) yy0=y1; if (yy0>y2) yy0=y2;
yy1=y0; if (yy1<y1) yy1=y1; if (yy1<y2) yy1=y2;
// fill with horizontal lines
for (y=yy0;y<=yy1;y++)
{
if (pl[y]<pr[y]) { xx0=pl[y]; xx1=pr[y]; }
else { xx1=pl[y]; xx0=pr[y]; }
for (x=xx0;x<=xx1;x++)
pyx[y][x]=col;
}
delete[] pl;
delete[] pr;
}
//---------------------------------------------------------------------------
example usage:
// init
gfx_main gfx;
gfx.resize(640,480);
// clear screen
TCanvas *scr=gfx.bmp->Canvas;
scr->Pen ->Color=clAqua;
scr->Font ->Color=clYellow;
scr->Brush->Color=clBlack;
scr->FillRect(TRect(0,0,xs,ys));
// triangle
troj(10,10,120,60,70,100,clAqua);
// here gfx.bmp holds the rendered image ...
Source is based on this:
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