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math/fixed: add I and P helper functions.

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The P function is especially common in e.g. Freetype code that works
with both the integer-pixel (X,Y) coordinates used by the stdlib image
package and sub-pixel (X,Y) coordinates used by its raster package.

Change-Id: I68be8ca71ceb24f40277ecc39a0896323f6671f5
Reviewed-on: https://go-review.googlesource.com/13652
Reviewed-by: Rob Pike <r@golang.org>
This commit is contained in:
Nigel Tao 2015-08-17 11:44:06 +10:00
parent b137518d47
commit d9c0088098
1 changed files with 14 additions and 0 deletions
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14
math/fixed/fixed.go
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@ -11,6 +11,13 @@ import (
// TODO: implement fmt.Formatter for %f and %g. // TODO: implement fmt.Formatter for %f and %g.
// I returns the integer value i as an Int26_6.
//
// For example, the integer value 2 is the Int26_6 128.
func I(i int) Int26_6 {
return Int26_6(i << 6)
}
// Int26_6 is a signed 26.6 fixed-point number. // Int26_6 is a signed 26.6 fixed-point number.
// //
// The integer part ranges from -33554432 to 33554431, inclusive. The // The integer part ranges from -33554432 to 33554431, inclusive. The
@ -58,6 +65,13 @@ func (x Int52_12) String() string {
return "-2251799813685248:0000" // The minimum value is -(1<<51). return "-2251799813685248:0000" // The minimum value is -(1<<51).
} }
// P returns the integer values x and y as a Point26_6.
//
// For example, the integer value pair (2, -3) is the Point26_6 (128, -192).
func P(x, y int) Point26_6 {
return Point26_6{Int26_6(x << 6), Int26_6(y << 6)}
}
// Point26_6 is a 26.6 fixed-point coordinate pair. // Point26_6 is a 26.6 fixed-point coordinate pair.
type Point26_6 struct { type Point26_6 struct {
X, Y Int26_6 X, Y Int26_6