Based on these guidelines I optimised Bresenhams line algorithm, it now fits for all kinds of line cases like images a, b, c, d, e, f, g, h show in those guidelines.
This is my test.txt input file for all line cases:
x1 y1 x2 y2 10 10 50 10 10 20 50 20 60 10 60 50 70 60 70 10 80 30 100 50 100 60 80 40 110 60 130 40 130 50 110 70 140 30 200 10 140 10 200 30 210 10 230 60 240 60 260 10
My code:
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <sstream>
#include<windows.h>
#include <cmath>
#include <iomanip>
using namespace std;
int main()
{
//Get a console handle
HWND myconsole = GetConsoleWindow();
//Get a handle to device context
HDC mydc = GetDC(myconsole);
//color
COLORREF COLOR = RGB(255, 255, 255);
int x1, y1, x2, y2;
ifstream fin("test.txt");
string line;
if (fin.is_open())
{
while (getline(fin, line))
{
stringstream S;
S << line; //store the line just read into the string stream
vector<int> thisLine(4, 0); //to save the numbers
for (int c(0); c<4; c++)
{
//use the string stream as a new input to put the data into a vector of int
S >> thisLine[c];
}
for (int c(0); c<4; c++) //set value for each variable
{
if (c == 0) { x1 = thisLine[c]; };
if (c == 1) { y1 = thisLine[c]; };
if (c == 2) { x2 = thisLine[c]; };
if (c == 3) { y2 = thisLine[c]; };
}
if (y1 == y2) //horizontal line
{
if (x1 > x2) {int x = x2; x2 = x1; x1 = x;}
for(x1; x1 <= x2; x1++)
{
SetPixel(mydc, x1, y1, COLOR);
}
}
if(x1 == x2) //vertical line
{
if (y1>y2) { int y = y2; y2 = y1; y1 = y; }
for (y1; y1 <= y2; y1++)
{
SetPixel(mydc, x1, y1, COLOR);
}
}
else
{ //bresenham line algorythm
int dx = abs(x2 - x1);
int dy = abs(y2 - y1);
int D = 2 * dy - dx;
int D1 = (2 * dy) - (2 * dx);
int D2 = 2 * dy;
double m = (double)(y2 - y1) / (x2 - x1);
if (x1 > x2) //switch numbers so line begin from left to right side
{
int x = x2;
x2 = x1;
x1 = x;
int y = y2;
y2 = y1;
y1 = y;
}
if (m == -1)
{
for (x1; x1 <= x2; x1++)
{
SetPixel(mydc, x1, y1, COLOR);
y1 = y1 - 1;
}
}
if (m == 1)
{
for (x1; x1 <= x2; x1++)
{
SetPixel(mydc, x1, y1, COLOR);
y1 = y1 + 1;
}
}
if (m> -1 && m<0)
{
for (x1; x1 <= x2; x1++)
{
if (D>0){
SetPixel(mydc, x1, y1, COLOR);
y1 = y1 - 1;
D = D + D1;
}
else{ SetPixel(mydc, x1, y1, COLOR); D = D + D2; }
}
}
if (m>0 && m<1)
{
for (x1; x1 <= x2; x1++)
{
if (D>0){
SetPixel(mydc, x1, y1, COLOR);
y1 = y1 + 1;
D = D + D1;
}
else{ SetPixel(mydc, x1, y1, COLOR); D = D + D2; }
}
}
if (m > 1) //rotate 90 degrees
{
int x11 = y1;
int x12 = y2;
y1 = x1;
y2 = x2;
x1 = x11;
x2 = x12;
int dx = abs(x2 - x1);
int dy = abs(y2 - y1);
int D = 2 * dy - dx;
int D1 = (2 * dy) - (2 * dx);
int D2 = 2 * dy;
for (x1; x1 <= x2; x1++)
{
if (D > 0) {
SetPixel(mydc, y1, x1, COLOR);
y1 = y1 + 1;
D = D + D1;
}
else{ SetPixel(mydc, y1, x1, COLOR); D = D + D2; }
}
}
if (m< -1) //rotate 90 degrees
{
int x11 = y1;
int x12 = y2;
y1 = x1;
y2 = x2;
x1 = x11;
x2 = x12;
int dx = abs(x2 - x1);
int dy = abs(y2 - y1);
int D = 2 * dy - dx;
int D1 = (2 * dy) - (2 * dx);
int D2 = 2 * dy;
for (x1; x1 >= x2; x1--)
{
if (D>0) {
SetPixel(mydc, y1, x1, COLOR);
y1 = y1 + 1;
D = D + D1;
}
else{ SetPixel(mydc, y1, x1, COLOR); D = D + D2; }
}
}
}
}
ReleaseDC(myconsole, mydc);
cin.ignore(); //nedrikst but cout
}
else
{
cout << "File could not be opened." << endl;
}
return 0;
}
But my question is: can I do this in a more effective way? If I had a million coordinates would it help to write my code differently? I mean like creating functions for all line cases not just an if with long case code or something like that.
I am hoping for suggestions that improve the performance. I am also interested in examples where code would execute slower (like in what case I could write code worse than this...).
