fix opacity jitter

data/shaders/stroke.glsl

@@ -100,11 +100,11 @@ void main()
         fg.rgb = mix(fg.rgb, mbg.rgb, mix_alpha * mbg.a);
     }
 
-    mediump float contribution = (opacity - bg.a) * fg.a;
+    mediump float contribution = max(0.0, opacity - bg.a) * fg.a;
     mediump float alpha_tot = bg.a + contribution;
-    mediump vec3 rgb = mix(bg.rgb, fg.rgb, fg.a / alpha_tot);
+    mediump vec3 rgb = mix(bg.rgb, fg.rgb, clamp(fg.a / alpha_tot, 0.0, 1.0));
     mediump vec4 frag_wet = vec4(rgb, max(bg.a, fg.a * 1.2));
-    mediump vec4 frag_dry = vec4(rgb, min(alpha_tot, opacity));
+    mediump vec4 frag_dry = vec4(rgb, alpha_tot);
     frag = mix(frag_dry, frag_wet, wet);
 }
 

src/shader.cpp

@@ -330,9 +330,9 @@ bool ShaderManager::load(kShader id, const std::string& path)
 
 bool ShaderManager::reload()
 {
-    bool success = true;
+    bool success = false;
     for (auto& s : m_shaders)
-        success &= s.second.reload();
+        success |= s.second.reload();
     return success;
 }