xfree86: Fix rotation of 2-color non-interleaved cursor images

When RandR 1.2's transformation code is enabled, it rotates the cursor
image so that it appears upright on a rotated screen.  This code
completely mangles 2-color cursors on hardware where the the mask and
source images are not interleaved due to two problems:

1. stride is calculated as (width / 4) rather than (width / 8), so the
   expression (y * stride) skips two lines instead of one for every
   time y is incremented.
2. cursor_bitpos ignores the 'mask' parameter if the hardware doesn't
   specify any of the HARDWARE_CURSOR_SOURCE_MASK_INTERLEAVE_* flags.

To fix this, refactor the code to pass the whole xf86CursorInfoPtr
through to cursor_bitpos and compute the correct stride there based on
the flags.  If none of the SOURCE_MASK_INTERLEAVE flags are set, use
the total cursor size to move the 'image' variable into the mask part
of the image before computing the desired byte pointer.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Reviewed-by: Robert Morell <rmorell@nvidia.com>
Reviewed-by: Alex Deucher <alexdeucher@gmail.com>
Tested-by: Cyril Brulebois <kibi@debian.org>

hw/xfree86/modes/xf86Cursors.c

@@ -1,5 +1,6 @@
 /*
  * Copyright © 2007 Keith Packard
+ * Copyright © 2010 Aaron Plattner
  *
  * Permission to use, copy, modify, distribute, and sell this software and its
  * documentation for any purpose is hereby granted without fee, provided that
@@ -126,12 +127,33 @@ xf86_crtc_rotate_coord_back (Rotation    rotation,
     *y_src = y_dst;
 }
 
+struct cursor_bit {
+    CARD8 *byte;
+    char bitpos;
+};
+
 /*
  * Convert an x coordinate to a position within the cursor bitmap
  */
-static int
+static struct cursor_bit
-cursor_bitpos (int flags, int x, Bool mask)
+cursor_bitpos (CARD8 *image, xf86CursorInfoPtr cursor_info, int x, int y,
+	       Bool mask)
 {
+    const int flags = cursor_info->Flags;
+    const Bool interleaved =
+	!!(flags & (HARDWARE_CURSOR_SOURCE_MASK_INTERLEAVE_1 |
+		    HARDWARE_CURSOR_SOURCE_MASK_INTERLEAVE_8 |
+		    HARDWARE_CURSOR_SOURCE_MASK_INTERLEAVE_16 |
+		    HARDWARE_CURSOR_SOURCE_MASK_INTERLEAVE_32 |
+		    HARDWARE_CURSOR_SOURCE_MASK_INTERLEAVE_64));
+    const int width = cursor_info->MaxWidth;
+    const int height = cursor_info->MaxHeight;
+    const int stride = interleaved ? width / 4 : width / 8;
+
+    struct cursor_bit ret;
+
+    image += y * stride;
+
     if (flags & HARDWARE_CURSOR_SWAP_SOURCE_AND_MASK)
 	mask = !mask;
     if (flags & HARDWARE_CURSOR_NIBBLE_SWAPPED)
@@ -149,29 +171,33 @@ cursor_bitpos (int flags, int x, Bool mask)
 	x = ((x & ~31) << 1) | (mask << 5) | (x & 31);
     else if (flags & HARDWARE_CURSOR_SOURCE_MASK_INTERLEAVE_64)
 	x = ((x & ~63) << 1) | (mask << 6) | (x & 63);
-    return x;
+    else if (mask)
+	image += stride * height;
+
+    ret.byte = image + (x / 8);
+    ret.bitpos = x & 7;
+
+    return ret;
 }
 
 /*
  * Fetch one bit from a cursor bitmap
  */
 static CARD8
-get_bit (CARD8 *image, int stride, int flags, int x, int y, Bool mask)
+get_bit (CARD8 *image, xf86CursorInfoPtr cursor_info, int x, int y, Bool mask)
 {
-    x = cursor_bitpos (flags, x, mask);
+    struct cursor_bit bit = cursor_bitpos(image, cursor_info, x, y, mask);
-    image += y * stride;
+    return (*bit.byte >> bit.bitpos) & 1;
-    return (image[(x >> 3)] >> (x & 7)) & 1;
 }
 
 /*
  * Set one bit in a cursor bitmap
  */
 static void
-set_bit (CARD8 *image, int stride, int flags, int x, int y, Bool mask)
+set_bit (CARD8 *image, xf86CursorInfoPtr cursor_info, int x, int y, Bool mask)
 {
-    x = cursor_bitpos (flags, x, mask);
+    struct cursor_bit bit = cursor_bitpos(image, cursor_info, x, y, mask);
-    image += y * stride;
+    *bit.byte |= 1 << bit.bitpos;
-    image[(x >> 3)] |= 1 << (x & 7);
 }
     
 /*
@@ -186,7 +212,6 @@ xf86_crtc_convert_cursor_to_argb (xf86CrtcPtr crtc, unsigned char *src)
     CARD32		*cursor_image = (CARD32 *) xf86_config->cursor_image;
     int			x, y;
     int			xin, yin;
-    int			stride = cursor_info->MaxWidth >> 2;
     int			flags = cursor_info->Flags;
     CARD32		bits;
 
@@ -201,10 +226,10 @@ xf86_crtc_convert_cursor_to_argb (xf86CrtcPtr crtc, unsigned char *src)
 				    cursor_info->MaxWidth,
 				    cursor_info->MaxHeight,
 				    x, y, &xin, &yin);
-	    if (get_bit (src, stride, flags, xin, yin, TRUE) ==
+	    if (get_bit (src, cursor_info, xin, yin, TRUE) ==
 		((flags & HARDWARE_CURSOR_INVERT_MASK) == 0))
 	    {
-		if (get_bit (src, stride, flags, xin, yin, FALSE))
+		if (get_bit (src, cursor_info, xin, yin, FALSE))
 		    bits = xf86_config->cursor_fg;
 		else
 		    bits = xf86_config->cursor_bg;
@@ -407,7 +432,6 @@ xf86_crtc_load_cursor_image (xf86CrtcPtr crtc, CARD8 *src)
         int x, y;
     	int xin, yin;
 	int stride = cursor_info->MaxWidth >> 2;
-	int flags = cursor_info->Flags;
 	
 	cursor_image = xf86_config->cursor_image;
 	memset(cursor_image, 0, cursor_info->MaxHeight * stride);
@@ -419,10 +443,10 @@ xf86_crtc_load_cursor_image (xf86CrtcPtr crtc, CARD8 *src)
 					cursor_info->MaxWidth,
 					cursor_info->MaxHeight,
 					x, y, &xin, &yin);
-		if (get_bit(src, stride, flags, xin, yin, FALSE))
+		if (get_bit(src, cursor_info, xin, yin, FALSE))
-		    set_bit(cursor_image, stride, flags, x, y, FALSE);
+		    set_bit(cursor_image, cursor_info, x, y, FALSE);
-		if (get_bit(src, stride, flags, xin, yin, TRUE))
+		if (get_bit(src, cursor_info, xin, yin, TRUE))
-		    set_bit(cursor_image, stride, flags, x, y, TRUE);
+		    set_bit(cursor_image, cursor_info, x, y, TRUE);
 	    }
     }
     crtc->funcs->load_cursor_image (crtc, cursor_image);