Drawing Straight Line using DDA Algorithm in C/C++

The digital differentia analyzer (DDA) is a scan-conversion line algorithm. In this algorithm, we sample the line at unit intervals in one coordinate and determine corresponding integer values nearest the line path of the other coordinate and plot those coordinate (pixel) in computer screen. Consider first a line with positive slope. If the slope is less than or equal to 1, we sample at unit x intervals (dx = 1) and computer each successive y value as y(k+1) = y(k) + m. Subscript k takes integer values starting from 1, for the first point, and increases by 1 until the final endpoint is reached. For lines with a positive slope greater than 1, we reverse the roles of x and y.That is, we sample at unit y intervals (dy = 1) and calculate each succeeding x value as x(k+1) = x(k) + (1/m)


The following section implements DDA Algorithm in C/C++. The source code is complied using gcc Compiler and Code::Blocks IDE. To print a pixel, SetPixel() function of windows.h is used.

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Note

To run this code in your machine with Code::blocks IDE, add a link library libgdi32.a (it is usually inside MinGWlib )  in linker setting and make the file extension .cpp but not .c. For C user, here is a link to download C file of this tutorial. Download

#include 
#include 
#define ROUND(a) ((int) (a + 0.5))
/* set window handle */
static HWND sHwnd;
static COLORREF redColor=RGB(255,0,0);
static COLORREF blueColor=RGB(0,0,255);
static COLORREF greenColor=RGB(0,255,0);
void SetWindowHandle(HWND hwnd){
sHwnd=hwnd;
}
/* SetPixel */
void setPixel(int x,int y,COLORREF& color=redColor){
if(sHwnd==NULL){
MessageBox(NULL,"sHwnd was not initialized !","Error",MB_OK|MB_ICONERROR);
exit(0);
}
HDC hdc=GetDC(sHwnd);
SetPixel(hdc,x,y,color);
ReleaseDC(sHwnd,hdc);
return;
// NEVERREACH //
}
void drawLineDDA(int xa, int ya, int xb, int yb){
int dx = xb - xa, dy = yb - ya, steps, k;
float xIncrement, yIncrement, x = xa, y = ya;
if(abs(dx) > abs(dy)) steps = abs(dx);
else steps = abs(dy);
xIncrement = dx / (float) steps;
yIncrement = dy / (float) steps;
setPixel(ROUND(x), ROUND(y));
for(int k = 0; k 

 


The output of this program is looks like









DDA algorithm is faster than the direct use of equation y = mx + c however, the rounding operations and floating-point arithmetic makes it still time consuming. To overcome this limitation of DDA Algorithm, Bresenham discovered Bresenham’s Line Drawing Algorithm.
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