clear up wcmVirtualTabletSize() to make it easier to understand

2 files changed, 59 insertions, 25 deletions

diff --git a/src/xf86Wacom.c b/src/xf86Wacom.c
index efca491..dd66ec8 100644
--- a/src/xf86Wacom.c
+++ b/src/xf86Wacom.c
@@ -284,33 +284,65 @@ void wcmVirtualTabletPadding(LocalDevicePtr local)
 void wcmVirtualTabletSize(LocalDevicePtr local)
 {
 	WacomDevicePtr priv = (WacomDevicePtr)local->private;
-	int i, tabletSize;
 
 	if (!(priv->flags & ABSOLUTE_FLAG))
 	{
 		priv->sizeX = priv->bottomX - priv->topX;
 		priv->sizeY = priv->bottomY - priv->topY;
+		DBG(10, priv, "relative device, using size of %d/%d\n", priv->sizeX, priv->sizeY);
+
 		return;
 	}
+	/* given a three monitor setup
+	 *	        offset
+	 *  __________ /__________  __________
+	 * |          ||          ||          |
+	 * |          ||          ||          |
+	 * |    A     ||    B     ||    C     |
+	 * |__________||__________||__________|
+	 *
+	 * this function calculates the virtual size of the tablet by
+	 * mapping the actual size into an axis range that is all three
+	 * monitors in device coordinates taken together.
+	 * in the simplest case, with 3 identical monitors, sizeX would be
+	 * (3 * actual size).
+	 *
+	 * coments describe for example of screen_no = 1 (Screen B)
+	 */
 
+	/* This is the actual tablet size in device coords */
 	priv->sizeX = priv->bottomX - priv->topX - priv->tvoffsetX;
 	priv->sizeY = priv->bottomY - priv->topY - priv->tvoffsetY;
 
 	if ((priv->screen_no != -1) || (priv->twinview != TV_NONE) || (!priv->wcmMMonitor))
 	{
-		i = priv->currentScreen;
-
+		double width, height; /* screen width, height */
+		double offset; /* screen x or y offset from origin */
+		double remainder; /* screen remainer on right-most screens */
+		double tabletSize;
+		int screen = priv->currentScreen;
+
+		width = priv->screenBottomX[screen] - priv->screenTopX[screen];
+		offset = priv->screenTopX[screen];
 		tabletSize = priv->sizeX;
-		priv->sizeX += (int)(((double)priv->screenTopX[i] * tabletSize)
-			/ ((double)(priv->screenBottomX[i] - priv->screenTopX[i])) + 0.5);
-		priv->sizeX += (int)((double)((priv->maxWidth - priv->screenBottomX[i])
-			* tabletSize) / ((double)(priv->screenBottomX[i] - priv->screenTopX[i])) + 0.5);
+		/* width left over right of the screen */
+		remainder = priv->maxWidth - priv->screenBottomX[screen];
+
+		/* add screen A size in device coordinates */
+		priv->sizeX += (int)((offset * tabletSize) / width + 0.5);
+
+		/* add screen C size in device coordinates */
+		priv->sizeX += (int)((remainder * tabletSize) / width + 0.5);
 
 		tabletSize = priv->sizeY;
-		priv->sizeY += (int)((double)(priv->screenTopY[i] * tabletSize)
-			/ ((double)(priv->screenBottomY[i] - priv->screenTopY[i])) + 0.5);
-		priv->sizeY += (int)((double)((priv->maxHeight - priv->screenBottomY[i])
-			* tabletSize) / ((double)(priv->screenBottomY[i] - priv->screenTopY[i])) + 0.5);
+
+		offset = priv->screenTopY[screen];
+		height = priv->screenBottomY[screen] - priv->screenTopY[screen];
+		/* height left over bottom of the screen */
+		remainder = priv->maxHeight - priv->screenBottomY[screen];
+
+		priv->sizeY += (int)(offset * tabletSize / height + 0.5);
+		priv->sizeY += (int)((remainder * tabletSize) / height + 0.5);
 	}
 	DBG(10, priv, "x=%d y=%d \n", priv->sizeX, priv->sizeY);
 	return;
diff --git a/src/xf86WacomDefs.h b/src/xf86WacomDefs.h
index 539a1e9..baddf1d 100644
--- a/src/xf86WacomDefs.h
+++ b/src/xf86WacomDefs.h
@@ -151,26 +151,28 @@ struct _WacomDeviceRec
 	int debugLevel;
 
 	unsigned int flags;	/* various flags (type, abs, touch...) */
-	int topX;		/* X top */
-	int topY;		/* Y top */
-	int bottomX;		/* X bottom */
-	int bottomY;		/* Y bottom */
+	int topX;		/* X top in device coords*/
+	int topY;		/* Y top in device coords*/
+	int bottomX;		/* X bottom in device coords*/
+	int bottomY;		/* Y bottom in device coords*/
 	int resolX;             /* X resolution */
 	int resolY;             /* Y resolution */
 	int maxX;	        /* tool logical maxX */
 	int maxY;	        /* tool logical maxY */
-	int sizeX;		/* active X size */
-	int sizeY;		/* active Y size */
+	int sizeX;		/* active X size in device coords */
+	int sizeY;		/* active Y size in device coords */
 	double factorX;		/* X factor */
 	double factorY;		/* Y factor */
 	unsigned int serial;	/* device serial number */
 	int screen_no;		/* associated screen */
-	int screenTopX[32];	/* left cordinate of the associated screen */
-	int screenTopY[32];	/* top cordinate of the associated screen */
-	int screenBottomX[32];	/* right cordinate of the associated screen */
-	int screenBottomY[32];	/* bottom cordinate of the associated screen */
-	int maxWidth;		/* max active screen width */
-	int maxHeight;		/* max active screen height */
+        /* The next 4 are set from the TVResolution coordinates if TwinView
+         * is active */
+	int screenTopX[32];	/* left cordinate of the associated screen in screen coords */
+	int screenTopY[32];	/* top cordinate of the associated screen in screen coords */
+	int screenBottomX[32];	/* right cordinate of the associated screen in screen coords */
+	int screenBottomY[32];	/* bottom cordinate of the associated screen in screen coords */
+	int maxWidth;		/* max active screen width in screen coords */
+	int maxHeight;		/* max active screen height in screen coords */
 	int leftPadding;	/* left padding for virtual tablet */
 	int topPadding;		/* top padding for virtual tablet */
 	int button[WCM_MAX_BUTTONS];/* buttons assignments */
@@ -221,8 +223,8 @@ struct _WacomDeviceRec
 	int numScreen;          /* number of configured screens */
 	int currentScreen;      /* current screen in display */
 	int twinview;	        /* using twinview mode of gfx card */
-	int tvoffsetX;		/* X edge offset for TwinView setup */
-	int tvoffsetY;		/* Y edge offset for TwinView setup */
+	int tvoffsetX;		/* X edge offset for TwinView setup in device coords  */
+	int tvoffsetY;		/* Y edge offset for TwinView setup in device coords */
 	int tvResolution[4];	/* twinview screens' resultion */
 	int wcmMMonitor;        /* disable/enable moving across screens in multi-monitor desktop */
 	int wcmDevOpenCount;    /* Device open count */