Fix a regression in the previous release that caused the cursor trail to not be hidden properly

In refactoring the trail shader, I guess I forgot to premultiply the
output color.

Fixes #9039

docs/changelog.rst

@@ -155,6 +155,9 @@ Detailed list of changes
   picker list the sessions in a fixed order rather than by most recent
   (:disc:`9033`)
 
+- Fix a regression in the previous release that caused the cursor trail to not
+  be hidden properly (:iss:`9039`)
+
 - Session files: Fix a regression in the previous release that broke matching on
   windows in the current tab (:iss:`9037`)
 

kitty/shaders.c

@@ -1231,7 +1231,7 @@ draw_cursor_trail(CursorTrail *trail, Window *active_window) {
     }
     color_vec3(trail_program_layout.uniforms.trail_color, trail_color);
 
-    glUniform1fv(trail_program_layout.uniforms.trail_opacity, 1, &trail->opacity);
+    glUniform1f(trail_program_layout.uniforms.trail_opacity, trail->opacity);
 
     draw_quad(true, 0);
     unbind_program();

kitty/trail_fragment.glsl

@@ -12,5 +12,5 @@ void main() {
     float in_x = step(cursor_edge_x[0], frag_pos.x) * step(frag_pos.x, cursor_edge_x[1]);
     float in_y = step(cursor_edge_y[1], frag_pos.y) * step(frag_pos.y, cursor_edge_y[0]);
     opacity *= 1.0f - in_x * in_y;
-    final_color = vec4(trail_color, opacity);
+    final_color = vec4(trail_color * opacity, opacity);
 }