头歌——计算机图形学——三角形填充

CG2-v2.0-三角形填充

第一关.扫描线填充法

一. 任务描述

1. 本关任务

了解和掌握扫描线填充法，实现对三角形区域进行填充，具体要求如下： (1) 补全triangle函数; (2) 将main函数中的三角形顶点坐标和triangle函数参数补充完整。

2. 输入

(1) 三角形的三个顶点的坐标:
t0 = {125,50}， t1 = {300,200}， t2 ={200,350};
(2) 三角形区域为蓝色。

3. 输出程序运行结果为一个蓝色三角形区域，如下图所示：

#include "pngimage.h"
#include<stdio.h>
#include <iostream>

struct Vec2i
{
	int x, y;
};

void triangle(Vec2i t0, Vec2i t1, Vec2i t2, PNGImage& image, PNGColor color) {
    // Please add your code here
    /********** Begin ********/ 

    
    if (t0.y>t1.y) std::swap(t0, t1); 
    if (t0.y>t2.y) std::swap(t0, t2); 
    if (t1.y>t2.y) std::swap(t1, t2);
    int total_height = t2.y-t0.y;
        for (int y=t0.y; y<=t1.y; y++) { 
        int segment_height = t1.y-t0.y+1;    //be careful with divisions by zero
        float alpha = (float)(y-t0.y)/total_height;      //edge t0t2
        float beta  = (float)(y-t0.y)/segment_height;    //edge t0t1 
        Vec2i A,B;
        A.y=B.y=y;
        A.x = t0.x + (t2.x-t0.x)*alpha; 
        B.x = t0.x + (t1.x-t0.x)*beta; 
        if (A.x>B.x) std::swap(A.x, B.x); 
        for (int x=A.x; x<=B.x; x++) { 
            image.set(x, y, color);  
        } 
    }
    for (int y = t1.y; y <= t2.y; y++)//感觉这个就是上半部分。

    {
        int segment_height = t2.y-t1.y+1;    
        float alpha2 = (float)(y-t0.y)/total_height;      //edge t0t2
        float beta2  = (float)(y-t1.y)/segment_height;    //edge t0t1 
        Vec2i A2,B2;
        A2.y=B2.y=y;
        A2.x = t0.x + (t2.x-t0.x)*alpha2; 
        B2.x = t1.x - (t1.x-t2.x)*beta2; 
        if (A2.x>