[gnome-shell] st: Rename and fix blur sampling calculation

[Marge Bot <marge-bot src gnome org>]

commit fe90da82b40da68e335cdb960a7b1d94400388be
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Thu Dec 17 02:03:34 2020 -0300

    st: Rename and fix blur sampling calculation
    
    What the blur shader does is going n_steps in each direction (e.g. in case
    we're in the horizontal pass that means left and right direction), sampling
    the adjacent texels of the texel we're currently blurring. That means
    n_steps actually is the amount of texels we're sampling in one direction,
    not in both directions.
    
    Make n_steps match what the blur shader does, and rename it to sampling_radius
    to match what it really means. Do that for both st-theme-node-drawing.c and
    st-private.c
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1542>

 src/st/st-private.c            | 19 +++++++++----------
 src/st/st-theme-node-drawing.c |  2 +-
 2 files changed, 10 insertions(+), 11 deletions(-)
---
diff --git a/src/st/st-private.c b/src/st/st-private.c
index 4d8952f5eb..83c0cac765 100644
--- a/src/st/st-private.c
+++ b/src/st/st-private.c
@@ -390,11 +390,10 @@ _st_create_shadow_pipeline (StShadow    *shadow_spec,
   CoglFramebuffer *fb;
   CoglPipeline *pipeline;
   CoglTexture *texture;
-  double sigma;
+  float sampling_radius;
+  float sigma;
   int src_height, dst_height;
   int src_width, dst_width;
-  int n_values;
-  int half;
 
   static CoglPipeline *shadow_pipeline_template = NULL;
 
@@ -402,13 +401,12 @@ _st_create_shadow_pipeline (StShadow    *shadow_spec,
   g_return_val_if_fail (src_texture != NULL, NULL);
 
   sigma = shadow_spec->blur / 2.f;
-  n_values = ceil (3 * sigma);
-  half = n_values / 2;
+  sampling_radius = ceilf (1.5 * sigma) * 2.0;
 
   src_width = cogl_texture_get_width (src_texture);
   src_height = cogl_texture_get_height (src_texture);
-  dst_width = src_width + 2 * half;
-  dst_height = src_height + 2 * half;
+  dst_width = src_width + 2 * sampling_radius;
+  dst_height = src_height + 2 * sampling_radius;
 
   texture = cogl_texture_2d_new_with_size (ctx, dst_width, dst_height);
   if (!texture)
@@ -442,9 +440,10 @@ _st_create_shadow_pipeline (StShadow    *shadow_spec,
   clutter_paint_node_add_child (blur_node, texture_node);
   clutter_paint_node_add_rectangle (texture_node,
                                     &(ClutterActorBox) {
-                                      half, half,
-                                      src_width + half,
-                                      src_height + half,
+                                      .x1 = sampling_radius,
+                                      .y1 = sampling_radius,
+                                      .x2 = src_width + sampling_radius,
+                                      .y2 = src_height + sampling_radius,
                                     });
 
   paint_context =
diff --git a/src/st/st-theme-node-drawing.c b/src/st/st-theme-node-drawing.c
index 64f2d75184..6c52da839b 100644
--- a/src/st/st-theme-node-drawing.c
+++ b/src/st/st-theme-node-drawing.c
@@ -2035,7 +2035,7 @@ st_theme_node_paint_sliced_shadow (StThemeNodePaintState *state,
   if (box_shadow_spec->blur == 0)
     shadow_blur_radius = 0;
   else
-    shadow_blur_radius = (5 * (box_shadow_spec->blur / 2.0)) / 2;
+    shadow_blur_radius = ceilf (1.5 * box_shadow_spec->blur / 2.0) * 2.0;
 
   shadow_width = state->box_shadow_width + 2 * shadow_blur_radius;
   shadow_height = state->box_shadow_height + 2 * shadow_blur_radius;