qxl: stride fixup

spice uses negative stride value to signal the bitmap is upside down.
The qxl renderer (used for scl, vnc and screenshots) wants a positive
value because it is easier to work with.  The positive value is then
stored in the very same variable, which has the drawback that the
upside-down test works only once.  Fix by using two variables.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

hw/qxl-render.c

@@ -28,16 +28,16 @@ static void qxl_flip(PCIQXLDevice *qxl, QXLRect *rect)
     int len, i;
 
     src += (qxl->guest_primary.surface.height - rect->top - 1) *
-        qxl->guest_primary.stride;
-    dst += rect->top  * qxl->guest_primary.stride;
+        qxl->guest_primary.abs_stride;
+    dst += rect->top  * qxl->guest_primary.abs_stride;
     src += rect->left * qxl->guest_primary.bytes_pp;
     dst += rect->left * qxl->guest_primary.bytes_pp;
     len  = (rect->right - rect->left) * qxl->guest_primary.bytes_pp;
 
     for (i = rect->top; i < rect->bottom; i++) {
         memcpy(dst, src, len);
-        dst += qxl->guest_primary.stride;
-        src -= qxl->guest_primary.stride;
+        dst += qxl->guest_primary.abs_stride;
+        src -= qxl->guest_primary.abs_stride;
     }
 }
 
@@ -45,7 +45,8 @@ void qxl_render_resize(PCIQXLDevice *qxl)
 {
     QXLSurfaceCreate *sc = &qxl->guest_primary.surface;
 
-    qxl->guest_primary.stride = sc->stride;
+    qxl->guest_primary.qxl_stride = sc->stride;
+    qxl->guest_primary.abs_stride = abs(sc->stride);
     qxl->guest_primary.resized++;
     switch (sc->format) {
     case SPICE_SURFACE_FMT_16_555:
@@ -87,11 +88,11 @@ void qxl_render_update(PCIQXLDevice *qxl)
         qemu_free_displaysurface(vga->ds);
 
         qxl->guest_primary.data = memory_region_get_ram_ptr(&qxl->vga.vram);
-        if (qxl->guest_primary.stride < 0) {
+        if (qxl->guest_primary.qxl_stride < 0) {
             /* spice surface is upside down -> need extra buffer to flip */
-            qxl->guest_primary.stride = -qxl->guest_primary.stride;
-            qxl->guest_primary.flipped = g_malloc(qxl->guest_primary.surface.width *
-                                                     qxl->guest_primary.stride);
+            qxl->guest_primary.flipped =
+                g_malloc(qxl->guest_primary.surface.width *
+                         qxl->guest_primary.abs_stride);
             ptr = qxl->guest_primary.flipped;
         } else {
             ptr = qxl->guest_primary.data;
@@ -100,7 +101,7 @@ void qxl_render_update(PCIQXLDevice *qxl)
                __FUNCTION__,
                qxl->guest_primary.surface.width,
                qxl->guest_primary.surface.height,
-               qxl->guest_primary.stride,
+               qxl->guest_primary.qxl_stride,
                qxl->guest_primary.bytes_pp,
                qxl->guest_primary.bits_pp,
                qxl->guest_primary.flipped ? "yes" : "no");
@@ -108,7 +109,7 @@ void qxl_render_update(PCIQXLDevice *qxl)
             qemu_create_displaysurface_from(qxl->guest_primary.surface.width,
                                             qxl->guest_primary.surface.height,
                                             qxl->guest_primary.bits_pp,
-                                            qxl->guest_primary.stride,
+                                            qxl->guest_primary.abs_stride,
                                             ptr);
         dpy_resize(vga->ds);
     }

hw/qxl.h

@@ -48,7 +48,8 @@ typedef struct PCIQXLDevice {
         QXLSurfaceCreate surface;
         uint32_t       commands;
         uint32_t       resized;
-        int32_t        stride;
+        int32_t        qxl_stride;
+        uint32_t       abs_stride;
         uint32_t       bits_pp;
         uint32_t       bytes_pp;
         uint8_t        *data, *flipped;