ScaleViewportExt

2.x

DWORD ScaleViewportExt(hdc, nXNum, nXDenom, nYNum, nYDenom)
HDC hdc;	/* handle of device context	*/
int nXNum;	/* amount by which current x-extent is multiplied	*/
int nXDenom;	/* amount by which current x-extent is divided	*/
int nYNum;	/* amount by which current y-extent is multiplied	*/
int nYDenom;	/* amount by which current y-extent is divided	*/

The ScaleViewportExt function modifies the viewport extents relative to the current values.

Parameters

hdc

Identifies the device context.

nXNum

Specifies the amount by which to multiply the current x-extent.

nXDenom

Specifies the amount by which to divide the result of multiplying the current x-extent by the value of the nXNum parameter.

nYNum

Specifies the amount by which to multiply the current y-extent.

nYDenom

Specifies the amount by which to divide the result of multiplying the current y-extent by the value of the nYNum parameter.

Return Value

The low-order word of the return value contains the x-extent, in device units, of the previous viewport if the function is successful; the high-order word contains the y-extent.

Comments

The new viewport extents are calculated by multiplying the current extents by the given numerator and then dividing by the given denominator, as shown in the following formulas:

nXNewVE = (nXOldVE * nXNum) / nXDenom
nYNewVE = (nYOldVE * nYNum) / nYDenom

Example

The following example draws a rectangle that is 4 logical units high and 4 logical units wide. It then calls the ScaleViewportExt function and draws a rectangle that is 8 units by 8 units. Because of the viewport scaling, the second rectangle is the same size as the first.

HDC  hdc;
RECT rc;

GetClientRect(hwnd, &rc);
hdc = GetDC(hwnd);
SetMapMode(hdc, MM_ANISOTROPIC);

SetWindowExt(hdc, 10, 10);
SetViewportExt(hdc, rc.right, rc.bottom);
Rectangle(hdc, 3, 3, 7, 7);

ScaleViewportExt(hdc, 1, 2, 1, 2);
Rectangle(hdc, 6, 6, 14, 14);

ReleaseDC(hwnd, hdc);