Raise an exception when bluring a indexed surface.

Author: yunline

docs/reST/ref/transform.rst

@@ -211,6 +211,9 @@ Instead, always begin with the original image and scale to the desired size.)
 
    Returns the blurred surface using box blur algorithm.
 
+   This function does not work for indexed surfaces.
+   An exception will be thrown if the input is an indexed surface.
+
    .. versionadded:: 2.2.0
 
    .. ## pygame.transform.box_blur ##
@@ -223,6 +226,9 @@ Instead, always begin with the original image and scale to the desired size.)
    Returns the blurred surface using gaussian blur algorithm.
    Slower than `box_blur()`.
 
+   This function does not work for indexed surfaces.
+   An exception will be thrown if the input is an indexed surface.
+
    .. versionadded:: 2.2.0
 
    .. ## pygame.transform.gaussian_blur ##

src_c/transform.c

@@ -3242,6 +3242,10 @@ blur(pgSurfaceObject *srcobj, pgSurfaceObject *dstobj, int radius,
 
     src = pgSurface_AsSurface(srcobj);
 
+    if (src->format->palette) {
+        return RAISE(PyExc_ValueError, "Indexed surfaces connot be blurred.");
+    }
+
     if (!dstobj) {
         retsurf = newsurf_fromsurf(src, src->w, src->h);
         if (!retsurf)