C ++三角形栅格化 [英] C++ triangle rasterization

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本文介绍了C ++三角形栅格化的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我试图修复这个三角形光栅化器，但不能使它正常工作。 

  void DrawTriangle（Point2D p0，Point2D p1，Point2D p2）
 {
 Point2D Top，Middle，Bottom; 
 bool MiddleIsLeft; 
 
 if（p0.y  {
 if（p0.y< p2.y）// case：1，2 
 {
 if（p1.y  {
 Top = p0; 
 Middle = p1; 
 Bottom = p2; 
 MiddleIsLeft = true; 
} 
 else // case：2 
 {
 Top = p0; 
 Middle = p2; 
 Bottom = p1; 
 MiddleIsLeft = false; 
} 
} 
 else // case：5 
 {
 Top = p2; 
 Middle = p0; 
 Bottom = p1; 
 MiddleIsLeft = true; 
} 
} 
 else // case：3，4，6 
 {
 if（p0.y  {
 Top = p1; 
 Middle = p0; 
 Bottom = p2; 
 MiddleIsLeft = false; 
} 
 else // case：3，6 
 {
 if（p1.y< p2.y）// case：3 
 {
 Top = p1; 
 Middle = p2; 
 Bottom = p0; 
 MiddleIsLeft = true; 
} 
 else // case 6 
 {
 Top = p2; 
 Middle = p1; 
 Bottom = p0; 
 MiddleIsLeft = false; 
} 
} 
} 
 
 float xLeft，xRight; 
 xLeft = xRight = Top.x; 
 float mLeft，mRight; 
 //区域1 
 if（MiddleIsLeft）
 {
 mLeft =（Top.x  -  Middle.x）/（Top.y  -  Middle.y）; 
 mRight =（Top.x  -  Bottom.x）/（Top.y  -  Bottom.y）; 
} 
 else 
 {
 mLeft =（Top.x  -  Bottom.x）/（Top.y  -  Bottom.y）; 
 mRight =（Middle.x  -  Top.x）/（Middle.y  -  Top.y）; 
} 
 int finalY; 
 float Tleft，Tright; 
 for（int y = ceil（Top.y）; y<（int）Middle.y; y ++）
 {
 Tleft = float（Top.yy）/ -Middle.y）; 
 Tright = float（Top.y-y）/（Top.y-Bottom.y）; 
 for（int x = ceil（xLeft）; x <= ceil（xRight）-1; x ++）
 {
 FrameBuffer :: SetPixel（x，y，p0.r，p0 .g，p0.b）; 
 
} 
 xLeft + = mLeft; 
 xRight + = mRight; 
 finalY = y; 
} 
 
 //区域2 
 if（MiddleIsLeft）
 {
 mLeft =（Bottom.x  -  Middle.x）/ -  Middle.y）; 
} 
 else 
 {
 mRight =（Middle.x  -  Bottom.x）/（Middle.y  -  Bottom.y）; 
} 
 
 for（int y = Middle.y; y <= ceil（Bottom.y）-1; y ++）
 {
 Tleft = float Bottom.yy）/（Bottom.y-Middle.y）; 
 Tright = float（Top.y-y）/（Top.y-Bottom.y）; 
 for（int x = ceil（xLeft）; x <= ceil（xRight）-1; x ++）
 {
 FrameBuffer :: SetPixel（x，y，p0.r，p0 .g，p0.b）; 
} 
 xLeft + = mLeft; 
 xRight + = mRight; 
 
} 
}

它可以绘制形状。



当我禁用第二个区域时，所有这些奇怪的三角形消失。





线框模式完美，所以这消除了所有其他可能性其他



解决方案

我在你的实现中迷失了，但这里是我做的（我有一个稍微复杂的版本的任意凸多边形，只是三角形），我认为除了 Bresenham的算法，它很简单（实际上算法是简单）：

  #include< stddef.h> 
 #include< limits.h> 
 #include< stdlib.h> 
 #include< stdio.h> 
 #include< string.h> 
 #include< time.h> 
 
 #define SCREEN_HEIGHT 22 
 #define SCREEN_WIDTH 78 
 
 //模拟帧缓冲区
字符屏幕[SCREEN_HEIGHT] [SCREEN_WIDTH]; 
 
 void SetPixel（long x，long y，char color）
 {
 if（（x< 0）||（x> = SCREEN_WIDTH）|| 
（y< 0）||（y> = SCREEN_HEIGHT））
 {
 return; 
} 
 
屏幕[y] [x] =颜色; 
} 
 
 void Visualize（void）
 {
 long x，y; 
 
 for（y = 0; y< SCREEN_HEIGHT; y ++）
 {
 for（x = 0; x< SCREEN_WIDTH; x ++）
 {
 printf（％c，Screen [y] [x]）; 
} 
 
 printf（\\\
）; 
} 
} 
 
 typedef struct 
 {
 long x，y; 
 unsigned char color; 
} Point2D; 
 
 
 // min三角形内每一水平线的X和max X 
 long ContourX [SCREEN_HEIGHT] [2]; 
 
 #define ABS（x）（（x> = 0）？x：-x）
 
 //扫描三角形设置的一边min X和max X在ContourX [] [] 
 //（使用Bresenham的线描算法）。 
 void scanLine（long x1，long y1，long x2，long y2）
 {
 long sx，sy，dx1，dy1，dx2，dy2，x，y，m，n，k ，cnt; 
 
 sx = x2  -  x1; 
 sy = y2  -  y1; 
 
 if（sx> 0）dx1 = 1; 
 else if（sx< 0）dx1 = -1; 
 else dx1 = 0; 
 
 if（sy> 0）dy1 = 1; 
 else if（sy< 0）dy1 = -1; 
 else dy1 = 0; 
 
 m = ABS（sx）; 
 n = ABS（sy）; $ b $ d dx2 = dx1; 
 dy2 = 0; 
 
 if（m  {
 m = ABS（sy）; 
 n = ABS（sx）; 
 dx2 = 0; 
 dy2 = dy1; 
} 
 
 x = x1; y = y1; 
 cnt = m + 1; 
 k = n / 2; 
 
 while（cnt--）
 {
 if（（y> = 0）&&（y< SCREEN_HEIGHT））
 {
 if（x  if（x> ContourX [y] [1]）ContourX [y] [1] = x; 
} 
 
 k + = n; 
 if（k  {
 x + = dx2; 
 y + = dy2; 
} 
 else 
 {
 k- = m; 
 x + = dx1; 
 y + = dy1; 
} 
} 
} 
 
 void DrawTriangle（Point2D p0，Point2D p1，Point2D p2）
 {
 int y; 
 
 for（y = 0; y< SCREEN_HEIGHT; y ++）
 {
 ContourX [y] [0] = LONG_MAX; // min X 
 ContourX [y] [1] = LONG_MIN; // max X 
} 
 
 ScanLine（p0.x，p0.y，p1.x，p1.y）; 
 ScanLine（p1.x，p1.y，p2.x，p2.y）; 
 ScanLine（p2.x，p2.y，p0.x，p0.y）; 
 
 for（y = 0; y< SCREEN_HEIGHT; y ++）
 {
 if（ContourX [y] [1]> = ContourX [y] [0] 
 {
 long x = ContourX [y] [0]; 
 long len = 1 + ContourX [y] [1]  -  ContourX [y] [0]; 
 
 //可以绘制水平线而不是单个像素
 while（len--）
 {
 SetPixel（x ++，y，p0.color）; 
} 
} 
} 
} 
 
 int main（void）
 {
 Point2D p0，p1，p2; 
 
 //清除屏幕
 memset（Screen，''，sizeof（Screen））; 
 
 //生成随机trinagle坐标
 srand（（unsigned）time（NULL））; 
 
 p0.x = rand（）％SCREEN_WIDTH; 
 p0.y = rand（）％SCREEN_HEIGHT; 
 
 p1.x = rand（）％SCREEN_WIDTH 
 p1.y = rand（）％SCREEN_HEIGHT; 
 
 p2.x =兰特（）％SCREEN_WIDTH; 
 p2.y =兰特（）％SCREEN_HEIGHT; 
 
 //绘制三角形
 p0.color ='1'; 
 DrawTriangle（p0，p1，p2）; 
 
 //还绘制三角形的顶点
与setPixel（p0.x，p0.y，'*'）; 
与setPixel（p1.x，p1.y，'*'）; 
 SetPixel（p2.x，p2.y，'*'）; 
 
 Visualize（）; 
 
 return 0; 
}



输出：

  * 111111 
 1111111111111 
 111111111111111111 
 1111111111111111111111 
 111111111111111111111111111 
 11111111111111111111111111111111 
 111111111111111111111111111111111111 
 11111111111111111111111111111111111111111 
 111111111111111111111111111111111111111 * 
 11111111111111111111111111111111111 
 1111111111111111111111111111111 
 111111111111111111111111111 
 11111111111111111111111 
 1111111111111111111 
 11111111111111 
 11111111111 
 1111111 
 1 *


I'm trying to fix this triangle rasterizer, but cannot make it work correctly. For some reason it only draws half of the triangles.

void DrawTriangle(Point2D p0, Point2D p1, Point2D p2)
{
    Point2D Top, Middle, Bottom;
    bool MiddleIsLeft;

    if (p0.y < p1.y)                    // case: 1, 2, 5
    {
        if (p0.y < p2.y)                // case: 1, 2
        {
            if (p1.y < p2.y)            // case: 1
            {
                Top = p0;
                Middle = p1;
                Bottom = p2;
                MiddleIsLeft = true;
            }
            else                        // case: 2
            {
                Top = p0;
                Middle = p2;
                Bottom = p1;
                MiddleIsLeft = false;
            }
        }
        else                            // case: 5
        {
            Top = p2;
            Middle = p0;
            Bottom = p1;
            MiddleIsLeft = true;                
        }
    }
    else                        // case: 3, 4, 6
    {
        if (p0.y < p2.y)        // case: 4
        {
            Top = p1;
            Middle = p0;
            Bottom = p2;
            MiddleIsLeft = false;
        }
        else                    // case: 3, 6
        {
            if (p1.y < p2.y)    // case: 3
            {
                Top = p1;
                Middle = p2;
                Bottom = p0;
                MiddleIsLeft = true;
            }
            else                // case 6
            {
                Top = p2;
                Middle = p1;
                Bottom = p0;
                MiddleIsLeft = false;
            }
        }
    }

    float xLeft, xRight;
    xLeft = xRight = Top.x;
    float mLeft, mRight;
    // Region 1
    if(MiddleIsLeft)
    {
        mLeft = (Top.x - Middle.x) / (Top.y - Middle.y);
        mRight = (Top.x - Bottom.x) / (Top.y - Bottom.y);
    }
    else
    {
        mLeft = (Top.x - Bottom.x) / (Top.y - Bottom.y);
        mRight = (Middle.x - Top.x) / (Middle.y - Top.y);
    }
    int finalY;
    float Tleft, Tright;
    for (int y = ceil(Top.y); y < (int)Middle.y; y++)
    {        
        Tleft=float(Top.y-y)/(Top.y-Middle.y);
        Tright=float(Top.y-y)/(Top.y-Bottom.y);
        for (int x = ceil(xLeft); x <= ceil(xRight) - 1 ; x++)
        {
            FrameBuffer::SetPixel(x, y, p0.r,p0.g,p0.b);

        }  
        xLeft += mLeft;
        xRight += mRight;
        finalY = y;
    }

    // Region 2 
    if (MiddleIsLeft)
    {
        mLeft = (Bottom.x - Middle.x) / (Bottom.y - Middle.y);
    }
    else
    {
        mRight = (Middle.x - Bottom.x) / (Middle.y - Bottom.y);
    }

    for (int y = Middle.y; y <= ceil(Bottom.y) - 1; y++)
    {
        Tleft=float(Bottom.y-y)/(Bottom.y-Middle.y);
        Tright=float(Top.y-y)/(Top.y-Bottom.y);
        for (int x = ceil(xLeft); x <= ceil(xRight) - 1; x++)
        {
            FrameBuffer::SetPixel(x, y, p0.r,p0.g,p0.b);
        }
        xLeft += mLeft;
        xRight += mRight; 

    }
}

Here is what happens when I use it to draw shapes.

When I disable the second region, all those weird triangles disappear.

The wireframe mode works perfect, so this eliminates all the other possibilities other than the triangle rasterizer.

解决方案

I kind of got lost in your implementation, but here's what I do (I have a slightly more complex version for arbitrary convex polygons, not just triangles) and I think apart from the Bresenham's algorithm it's very simple (actually the algorithm is simple too):

#include <stddef.h>
#include <limits.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <time.h>

#define SCREEN_HEIGHT 22
#define SCREEN_WIDTH  78

// Simulated frame buffer
char Screen[SCREEN_HEIGHT][SCREEN_WIDTH];

void SetPixel(long x, long y, char color)
{
  if ((x < 0) || (x >= SCREEN_WIDTH) ||
      (y < 0) || (y >= SCREEN_HEIGHT))
  {
    return;
  }

  Screen[y][x] = color;
}

void Visualize(void)
{
  long x, y;

  for (y = 0; y < SCREEN_HEIGHT; y++)
  {
    for (x = 0; x < SCREEN_WIDTH; x++)
    {
      printf("%c", Screen[y][x]);
    }

    printf("\n");
  }
}

typedef struct
{
  long x, y;
  unsigned char color;
} Point2D;


// min X and max X for every horizontal line within the triangle
long ContourX[SCREEN_HEIGHT][2];

#define ABS(x) ((x >= 0) ? x : -x)

// Scans a side of a triangle setting min X and max X in ContourX[][]
// (using the Bresenham's line drawing algorithm).
void ScanLine(long x1, long y1, long x2, long y2)
{
  long sx, sy, dx1, dy1, dx2, dy2, x, y, m, n, k, cnt;

  sx = x2 - x1;
  sy = y2 - y1;

  if (sx > 0) dx1 = 1;
  else if (sx < 0) dx1 = -1;
  else dx1 = 0;

  if (sy > 0) dy1 = 1;
  else if (sy < 0) dy1 = -1;
  else dy1 = 0;

  m = ABS(sx);
  n = ABS(sy);
  dx2 = dx1;
  dy2 = 0;

  if (m < n)
  {
    m = ABS(sy);
    n = ABS(sx);
    dx2 = 0;
    dy2 = dy1;
  }

  x = x1; y = y1;
  cnt = m + 1;
  k = n / 2;

  while (cnt--)
  {
    if ((y >= 0) && (y < SCREEN_HEIGHT))
    {
      if (x < ContourX[y][0]) ContourX[y][0] = x;
      if (x > ContourX[y][1]) ContourX[y][1] = x;
    }

    k += n;
    if (k < m)
    {
      x += dx2;
      y += dy2;
    }
    else
    {
      k -= m;
      x += dx1;
      y += dy1;
    }
  }
}

void DrawTriangle(Point2D p0, Point2D p1, Point2D p2)
{
  int y;

  for (y = 0; y < SCREEN_HEIGHT; y++)
  {
    ContourX[y][0] = LONG_MAX; // min X
    ContourX[y][1] = LONG_MIN; // max X
  }

  ScanLine(p0.x, p0.y, p1.x, p1.y);
  ScanLine(p1.x, p1.y, p2.x, p2.y);
  ScanLine(p2.x, p2.y, p0.x, p0.y);

  for (y = 0; y < SCREEN_HEIGHT; y++)
  {
    if (ContourX[y][1] >= ContourX[y][0])
    {
      long x = ContourX[y][0];
      long len = 1 + ContourX[y][1] - ContourX[y][0];

      // Can draw a horizontal line instead of individual pixels here
      while (len--)
      {
        SetPixel(x++, y, p0.color);
      }
    }
  }
}

int main(void)
{
  Point2D p0, p1, p2;

  // clear the screen
  memset(Screen, ' ', sizeof(Screen));

  // generate random trinagle coordinates
  srand((unsigned)time(NULL));

  p0.x = rand() % SCREEN_WIDTH;
  p0.y = rand() % SCREEN_HEIGHT;

  p1.x = rand() % SCREEN_WIDTH;
  p1.y = rand() % SCREEN_HEIGHT;

  p2.x = rand() % SCREEN_WIDTH;
  p2.y = rand() % SCREEN_HEIGHT;

  // draw the triangle
  p0.color = '1';
  DrawTriangle(p0, p1, p2);

  // also draw the triangle's vertices
  SetPixel(p0.x, p0.y, '*');
  SetPixel(p1.x, p1.y, '*');
  SetPixel(p2.x, p2.y, '*');

  Visualize();

  return 0;
}

Output:

   *111111
    1111111111111
      111111111111111111
         1111111111111111111111
           111111111111111111111111111
             11111111111111111111111111111111
                111111111111111111111111111111111111
                  11111111111111111111111111111111111111111
                    111111111111111111111111111111111111111*
                       11111111111111111111111111111111111
                         1111111111111111111111111111111
                            111111111111111111111111111
                              11111111111111111111111
                                1111111111111111111
                                   11111111111111
                                     11111111111
                                       1111111
                                          1*

这篇关于C ++三角形栅格化的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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