Crt, Ripple and Glitch take a level, 0 to 3, tunable at run time

Coordinator's request: `Crt 0..3` (likewise Ripple, Glitch), 0 off, `on`
the default level 2 (the polished rewrite), `off` and a bare word as
before. The level is one uniform (pardesLevel, beside pardesOpaque in the
prefix's own block); each pass picks its constants by it. Level 3 is at
least as strong as the old effects, measured as pixels changed by more
than 8 in a channel against a plain frame: Crt 18.3% (old 17.4%), Ripple
11.1% (9.5%), Glitch 9.3% a frame (8.1%); Glitch's level raises how often
it bursts as well as how hard. Config and ctl report `Crt 2` / `Crt off`.

Shared files touched: ninep/ctl.zig (the report line). Not touched:
pardes.zig, Messages.zig, mouse.zig, gui.zig, detached/*.

1 files changed, 9 insertions, 2 deletions

diff --git a/shaders/post/prefix.glsl b/shaders/post/prefix.glsl
index efa49483..e718a98f 100644
--- a/shaders/post/prefix.glsl
+++ b/shaders/post/prefix.glsl
@@ -39,12 +39,19 @@ layout(set = 3, binding = 0, std140) uniform Globals {
     uniform vec3  iSelectionBackgroundColor;
 };
 
-// pardes's own: 1 when the window is opaque, so a pass cannot punch holes
-// in it through its alpha.
+// pardes's own: pardesOpaque is 1 when the window is opaque, so a pass
+// cannot punch holes in it through its alpha; pardesLevel is a bundled
+// pass's strength, 1 to 3 (`Crt 3`), and 0 for a user's file.
 layout(set = 3, binding = 1, std140) uniform PardesPost {
     float pardesOpaque;
+    float pardesLevel;
 };
 
+// A bundled pass's constant at levels 1, 2 and 3.
+float pardesByLevel(float one, float two, float three) {
+    return pardesLevel < 1.5 ? one : (pardesLevel < 2.5 ? two : three);
+}
+
 #define CURSORSTYLE_BLOCK        0
 #define CURSORSTYLE_BLOCK_HOLLOW 1
 #define CURSORSTYLE_BAR          2