feat: Enhance background opacity handling and optimize pixel rendering for transparency

scripts/gui.lua

@@ -196,11 +196,16 @@ function Context:applyBackgroundOpacity(color)
     -- For full transparency (opacity = 0), set alpha to 0
     -- For partial transparency, multiply the existing alpha
     local result = {color[1], color[2], color[3], color[4] or 1.0}
+    local originalAlpha = result[4]
     if self.opacity == 0 then
         result[4] = 0
     else
         result[4] = result[4] * self.opacity
     end
+    if lua_debug then
+        print(string.format("[GUI] applyBackgroundOpacity: opacity=%.2f, original alpha=%.2f, new alpha=%.2f",
+                           self.opacity, originalAlpha, result[4]))
+    end
     return result
 end
 
@@ -208,6 +213,12 @@ function Context:pushRect(rect, params)
     params = params or {}
     -- Only apply opacity to the background color, not borders or other elements
     local color = params.color and self:applyBackgroundOpacity(params.color) or params.color
+
+    -- Skip drawing background rect entirely if it would be fully transparent
+    if color and color[4] == 0 and (not params.borderColor or params.borderWidth == 0) then
+        return
+    end
+
     local command = {
         type = "rect",
         x = rect.x,

src/services/impl/gui_renderer.cpp

@@ -5,6 +5,7 @@
 #include <cmath>
 #include <cctype>
 #include <cstdio>
+#include <cstring>
 #include <fstream>
 #include <iterator>
 #include <stdexcept>
@@ -479,12 +480,22 @@ GuiRenderer::GuiRenderer(VkDevice device, VkPhysicalDevice physicalDevice, VkFor
         const auto& pixels = canvas_->Pixels();
         size_t pixelCount = static_cast<size_t>(canvasWidth_) * canvasHeight_;
         uint8_t* dest = reinterpret_cast<uint8_t*>(stagingMapped_);
+
+        // Clear destination to fully transparent so pixels with alpha=0 don't overwrite the scene
+        std::memset(dest, 0, pixelCount * 4);
+
         for (size_t i = 0; i < pixelCount; ++i) {
             size_t offset = i * 4;
             uint8_t r = pixels[offset];
             uint8_t g = pixels[offset + 1];
             uint8_t b = pixels[offset + 2];
             uint8_t a = pixels[offset + 3];
+
+            // Skip fully transparent pixels to avoid overwriting the 3D scene
+            if (a == 0) {
+                continue;
+            }
+
             switch (swapchainFormat_) {
                 case VK_FORMAT_B8G8R8A8_UNORM:
                 case VK_FORMAT_B8G8R8A8_SRGB: