From c29c9fa826b7112156fd6150b5f1564227935c05 Mon Sep 17 00:00:00 2001
From: Siarhei Siamashka <siarhei.siamashka@nokia.com>
Date: Thu, 22 Oct 2009 05:27:33 +0300
Subject: [PATCH 3/6] Generic C implementation of pixman_blt with overlapping support

Uses memcpy/memmove functions to copy pixels, can handle the
case when both source and destination areas are in the same
image (this is useful for scrolling).

It is assumed that copying direction is only important when
using the same image for both source and destination (and
src_stride == dst_stride). Copying direction is undefined
for the images with different source and destination stride
which happen to be in the overlapped areas (but this is an
unrealistic case anyway).
---
 pixman/pixman-general.c |   21 ++++++++++++++++++---
 pixman/pixman-private.h |   43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/pixman/pixman-general.c b/pixman/pixman-general.c
index c96a3f9..d71a299 100644
--- a/pixman/pixman-general.c
+++ b/pixman/pixman-general.c
@@ -300,9 +300,24 @@ general_blt (pixman_implementation_t *imp,
              int                      width,
              int                      height)
 {
-    /* We can't blit unless we have sse2 or mmx */
-
-    return FALSE;
+    uint8_t *dst_bytes = (uint8_t *)dst_bits;
+    uint8_t *src_bytes = (uint8_t *)src_bits;
+    int bpp;
+
+    if (src_bpp != dst_bpp || src_bpp & 7)
+	return FALSE;
+
+    bpp = src_bpp >> 3;
+    width *= bpp;
+    src_stride *= 4;
+    dst_stride *= 4;
+    pixman_blt_helper (src_bytes + src_y * src_stride + src_x * bpp,
+                       dst_bytes + dst_y * dst_stride + dst_x * bpp,
+                       src_stride,
+                       dst_stride,
+                       width,
+                       height);
+    return TRUE;
 }
 
 static pixman_bool_t
diff --git a/pixman/pixman-private.h b/pixman/pixman-private.h
index 5000f91..8c5d4fd 100644
--- a/pixman/pixman-private.h
+++ b/pixman/pixman-private.h
@@ -10,6 +10,7 @@
 
 #include "pixman.h"
 #include <time.h>
+#include <string.h>
 #include <assert.h>
 
 #include "pixman-compiler.h"
@@ -794,4 +795,46 @@ void pixman_timer_register (pixman_timer_t *timer);
 
 #endif /* PIXMAN_TIMERS */
 
+/* a helper function, can blit 8-bit images with src/dst overlapping support */
+static inline void
+pixman_blt_helper (uint8_t *src_bytes,
+                   uint8_t *dst_bytes,
+                   int      src_stride,
+                   int      dst_stride,
+                   int      width,
+                   int      height)
+{
+    /*
+     * The second part of this check is not strictly needed, but it prevents
+     * unnecessary upside-down processing of areas which belong to different
+     * images. Upside-down processing can be slower with fixed-distance-ahead
+     * prefetch and perceived as having more tearing.
+     */
+    if (src_bytes < dst_bytes + width &&
+	src_bytes + src_stride * height > dst_bytes)
+    {
+	src_bytes += src_stride * height - src_stride;
+	dst_bytes += dst_stride * height - dst_stride;
+	dst_stride = -dst_stride;
+	src_stride = -src_stride;
+	/* Horizontal scrolling to the left needs memmove */
+	if (src_bytes + width > dst_bytes)
+	{
+	    while (--height >= 0)
+	    {
+		memmove (dst_bytes, src_bytes, width);
+		dst_bytes += dst_stride;
+		src_bytes += src_stride;
+	    }
+	    return;
+	}
+    }
+    while (--height >= 0)
+    {
+	memcpy (dst_bytes, src_bytes, width);
+	dst_bytes += dst_stride;
+	src_bytes += src_stride;
+    }
+}
+
 #endif /* PIXMAN_PRIVATE_H */
-- 
1.6.2.4