alpha: scale and clamp alpha to its full extend

Convert the alpha value to 0->255 when setting and to 0->256 when using as
a scaling factor. This makes sure we can reach the full opacity value of 0xff in
all cases.

1 files changed, 5 insertions, 3 deletions

diff --git a/gst/alpha/gstalpha.c b/gst/alpha/gstalpha.c
index 01bcbde8e..6aa1f8af5 100644
--- a/gst/alpha/gstalpha.c
+++ b/gst/alpha/gstalpha.c
@@ -212,2 +212,3 @@ gst_alpha_base_init (gpointer g_class)
 }
+
 static void
@@ -349,2 +350,3 @@ gst_alpha_set_property (GObject * object, guint prop_id,
 }
+
 static void
@@ -472,3 +474,3 @@ gst_alpha_set_ayuv (guint8 * src, guint8 * dest, gint width, gint height,
 {
-  gint b_alpha = (gint) (alpha * 255);
+  gint s_alpha = CLAMP ((gint) (alpha * 256), 0, 256);
   gint y, x;
@@ -477,3 +479,3 @@ gst_alpha_set_ayuv (guint8 * src, guint8 * dest, gint width, gint height,
     for (x = 0; x < width; x++) {
-      *dest++ = (*src++ * b_alpha) >> 8;
+      *dest++ = (*src++ * s_alpha) >> 8;
       *dest++ = *src++;
@@ -489,3 +491,3 @@ gst_alpha_set_i420 (guint8 * src, guint8 * dest, gint width, gint height,
 {
-  gint b_alpha = (gint) (alpha * 255);
+  gint b_alpha = CLAMP ((gint) (alpha * 255), 0, 255);
   guint8 *srcY;