Reducing matte frame width results in uneven rendering

[snwau]

Raised by Cho Seungbo on 9 January 2012 within Cocoa Controls comments:

When I set SWSnapshotStackViewMatteWidth = 3, the margin of left and top looks 3, but the margin of right and bottom is 2.

Suspect it's a rounding issue in frame calculations. As I round both the calculated matte frame and UIImage rectangle to make sure they are aligned appropriately for drawing to avoid unnecessary anti-aliasing (i.e. drawing between pixels, etc).
Lines are drawn on 0.5 point coordinates, UIImage drawn on integer coordinates.

Relates to known issue of using view with smaller frame sizes and scaling of effects to better suit.

[snwau]

Further information provided by Cho Seungbo on 10 January 2012:

I changed just these values

#define SWSnapshotStackViewMatteWidth 3.0

// SINGLE DISPLAY MODE CONSTANTS
//! Defines X offset for either edge to indent shadow effect (single mode)
#define SWSnapshotStackViewSingleShadowXOffset 0.0
//! Defines Y offset to drop shadow below snapshot matte frame
#define SWSnapshotStackViewSingleShadowYOffset 0.0
//! Defines radius of the shadow (results in magnitude and softness of shadow)
#define SWSnapshotStackViewSingleShadowRadius 1.0

and then I moved slider control of your sample app.

Actually, when I used original values, the margins are not same. Left and Top margin is bigger than
right and bottom margin. If you use small value for SWSnapshotStackViewMatteWidth, you can find
the gap of margin more easily.