# Bottom layer Algorithm for drawing

Source: Internet
Author: User

I usually use APIs, CDC, and encapsulated internal functions. It's easy to draw lines and circles...

I recently learned about computer graphics and had to study the underlying algorithms internally...

I will post a few codes here to share with you!

(Only the OnDraw function of MFC is provided here)

I. Three algorithms for draw lines:

1. DDA (numerical differentiation) method:

Void CDDALineView: OnDraw (CDC * pDC)

{

CDDALineDoc * pDoc = GetDocument ();

ASSERT_VALID (pDoc );

// TODO: add draw code for native data here

Int x, x0 (200), y0 (200), x1 (500), y1 (500 );

Float dx, dy, y, k;

Dx = x1-x0;

Dy = y1-y0;

K = dy/dx;

Y = y0;

For (x = x0; x <= x1; x ++)

{

PDC-> SetPixel (x, (int) (y + 0.5), RGB (, 0 ));

Y + = k;

}

}

2. midpoint draw Algorithm

Void CMidpointLineView: OnDraw (CDC * pDC)

{

CMidpointLineDoc * pDoc = GetDocument ();

ASSERT_VALID (pDoc );

// TODO: add draw code for native data here

Int a, B, d1, d2, d, x, y;

Int x0 (200), x1 (500), y0 (200), y1 (500 );

A = y0-y1;

B = x1-x0;

D = 2 * a + B;

D1 = 2 *;

D2 = 2 * (a + B );

X = x0;

Y = y0;

PDC-> SetPixel (x, y, RGB (0,255, 0 ));

While (x <x1)

{

If (d <0)

{

X ++;

Y ++;

D + = d2;

}

Else

{

X ++;

D + = d1;

}

PDC-> SetPixel (x, y, RGB (0,255, 0 ));

}

}

3. Bresenham algorithm:

Void CBresenhamline2View: OnDraw (CDC * pDC)

{

CBresenhamline2Doc * pDoc = GetDocument ();

ASSERT_VALID (pDoc );

// TODO: add draw code for native data here

Int x0 (200), y0 (200), x1 (500), y1 (500 );

Int x, y, dx, dy;

Dx = x1-x0;

Dy = y1-y0;

Int e =-dx;

X = x0;

Y = y0;

For (int I = 0; I <= dx; I ++)

{

PDC-> SetPixel (x, y, RGB (0, 255 ));

X = x + 1;

E = e + 2 * dy;

If (e> = 0)

{

Y ++;

E = E-2 * dx;

}

}

}

Ii. MidPoint Circle Algorithm:

Void CMidPointCircleView: OnDraw (CDC * pDC)

{

CMidPointCircleDoc * pDoc = GetDocument ();

ASSERT_VALID (pDoc );

// TODO: add draw code for native data here

Int r = 100; // radius

Int m (300), n (250); // coordinates of the center

Int x, y;

Float d;

X = 0;

Y = 0 + r;

D = 1.25-r;

// MidPoint Circle Algorithm

PDC-> SetPixel (m + x, n + y, RGB (255, 0 ));

PDC-> SetPixel (m + y, n + x, RGB (255, 0 ));

PDC-> SetPixel (m-x, n + y, RGB (255, 0 ));

PDC-> SetPixel (m + y, n-x, RGB (255, 0 ));

PDC-> SetPixel (m + x, n-y, RGB (255, 0 ));

PDC-> SetPixel (m-y, n + x, RGB (255, 0 ));

PDC-> SetPixel (m-x, n-y, RGB (255, 0 ));

PDC-> SetPixel (m-y, n-x, RGB (255, 0 ));

While (x <= y)

{

If (d <0)

D + = 2 * x + 3;

Else

{

D + = 2 * (x-y) + 5;

Y --;

}

X ++;

PDC-> SetPixel (m + x, n + y, RGB (255, 0 ));

PDC-> SetPixel (m + y, n + x, RGB (255, 0 ));

PDC-> SetPixel (m-x, n + y, RGB (255, 0 ));

PDC-> SetPixel (m + y, n-x, RGB (255, 0 ));

PDC-> SetPixel (m + x, n-y, RGB (255, 0 ));

PDC-> SetPixel (m-y, n + x, RGB (255, 0 ));

PDC-> SetPixel (m-x, n-y, RGB (255, 0 ));

PDC-> SetPixel (m-y, n-x, RGB (255, 0 ));

}

}

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