Legacy Document

Inside Macintosh: Imaging With QuickDraw /

Chapter 3 - QuickDraw Drawing / QuickDraw Drawing Reference

Routines / Scaling and Mapping Points, Rectangles, Polygons, and Regions

ScalePt

To scale a height and width according to the proportions of two rectangles, use the ScalePt procedure.

PROCEDURE ScalePt (VAR pt:\xDDPoint; srcRect,dstRect:\xDDRect);

pt

On input, an initial height and width (specified in the two fields of a Point record) to scale; upon completion, vertical and horizontal scaling factors derived by multiplying the height and width by ratios of the height and width of the rectangle in the srcRect parameter to the height and width of the rectangle in the dstRect parameter.

srcRect

A rectangle. The ratio of this rectangle's height to the height of the rectangle in the dstRect parameter provides the vertical scaling factor, and the ratio of this rectangle's width to the width of the rectangle in the dstRect parameter provides the horizontal scaling factor.

dstRect

A rectangle compared to the rectangle in the srcRect parameter to determine vertical and horizontal scaling factors.

DESCRIPTION

The ScalePt procedure produces horizontal and vertical scaling factors from the proportions of two rectangles. You can use ScalePt, for example, to scale the dimensions of the graphics pen.

You specify an initial height and width to scale in the pt parameter. This parameter is of type Point, although you don't pass coordinates in this parameter. Instead, you pass an initial height to scale in the v (or vertical) field of the Point record, and you pass an initial width to scale in the h (or horizontal) field.

The ScalePt procedure scales these measurements by multiplying the initial height you specify in the pt parameter by the ratio of the height of the rectangle you specify in the dstRect parameter to the height of the rectangle you specify in the srcRect parameter, and by multiplying the initial width in the pt parameter by the ratio of the width of the dstRect rectangle to the width of the srcRect rectangle. The ScalePt procedure returns the result in the pt parameter.

In Figure 3-23, where the width of the dstRect rectangle is twice the width of the srcRect rectangle, and its height is three times the height of srcRect, ScalePt scales the width of the graphics pen from 3 to 6 and scales its height from 2 to 6.

SPECIAL CONSIDERATIONS

The minimum value ScalePt returns is (1,1).

Figure 3-23 Using ScalePt and MapPt