update vignette calculation formula

res/shaders/screen.glslf

@@ -5,16 +5,15 @@ uniform sampler2D u_texture0;
 uniform ivec2 u_screenSize;
 
 // Vignette
-vec4 apply_vignette(vec4 color)
-{
+vec4 apply_vignette(vec4 color) {
     vec2 position = (gl_FragCoord.xy / u_screenSize) - vec2(0.5);
     float dist = length(position);
 
-    float radius = 2.0;
-    float softness = 1.7;
+    float radius = 1.3;
+    float softness = 1.0;
     float vignette = smoothstep(radius, radius - softness, dist);
 
-    color.rgb = color.rgb - (1.0 - vignette);
+    color.rgb = color.rgb * vignette;
 
     return color;
 }