fix(ui): preserve fractional button content centering (#4036)

* fix(ui): preserve fractional button centering

* Remove comments from button.cpp centering logic

Removed comments explaining the centering logic for button content alignment.

---------

Co-authored-by: Lemmy <studio@quadbyte.net>

Author: blackbartblues

meson.build

@@ -1123,6 +1123,7 @@ if build_tests
     'app_identity',
     'audio_glyphs',
     'battery_hook_state',
+    'button_layout',
     'cairo_text_renderer',
     'calendar_cache_permissions',
     'cli_help',

src/ui/controls/button.cpp

@@ -778,12 +778,12 @@ void Button::doLayout(Renderer& renderer) {
       const float contentHeight = contentBottom - contentTop;
       float targetLeft = 0.0F;
       if (m_contentAlign == ButtonContentAlign::Center) {
-        targetLeft = std::round((width() - contentWidth) * 0.5F);
+        targetLeft = (width() - contentWidth) * 0.5F;
       } else { // End
         targetLeft = std::round(Style::rtl() ? paddingLeft() : width() - contentWidth - paddingRight());
       }
       const float shiftX = targetLeft - contentLeft;
-      const float targetTop = std::round((height() - contentHeight) * 0.5F);
+      const float targetTop = (height() - contentHeight) * 0.5F;
       const float shiftY = targetTop - contentTop;
       if (std::abs(shiftX) > 0.01F || std::abs(shiftY) > 0.01F) {
         for (auto& child : children()) {

tests/button_layout_test.cpp

@@ -0,0 +1,92 @@
+#include "render/core/renderer.h"
+#include "render/core/texture_manager.h"
+#include "ui/controls/button.h"
+#include "ui/controls/glyph.h"
+
+#include <cmath>
+#include <cstdlib>
+#include <print>
+#include <string_view>
+#include <vector>
+
+namespace {
+
+  class StubRenderer final : public Renderer {
+  public:
+    TextMetrics measureText(
+        std::string_view, float fontSize, FontWeight, float, int, TextAlign, std::string_view, TextEllipsize, bool
+    ) override {
+      return TextMetrics{.bottom = fontSize};
+    }
+
+    TextMetrics measureFont(float fontSize, FontWeight) override { return TextMetrics{.bottom = fontSize}; }
+
+    void measureTextCursorStops(
+        std::string_view, float, const std::vector<std::size_t>&, std::vector<float>&, FontWeight
+    ) override {}
+
+    void measureTextCursorStopsWrapped(
+        std::string_view, float, const std::vector<std::size_t>&, float, std::vector<TextCursorStop>&, FontWeight
+    ) override {}
+
+    TextMetrics measureGlyph(char32_t, float) override {
+      return TextMetrics{
+          .width = 18.0F,
+          .left = 1.5F,
+          .right = 19.5F,
+          .top = -15.0F,
+          .bottom = 3.0F,
+          .inkTop = -15.0F,
+          .inkBottom = 3.0F,
+          .inkLeft = 1.5F,
+          .inkRight = 19.5F,
+      };
+    }
+
+    TextureManager& textureManager() override { std::abort(); }
+    [[nodiscard]] float renderScale() const noexcept override { return 1.0F; }
+  };
+
+  bool near(float actual, float expected) { return std::abs(actual - expected) < 0.001F; }
+
+} // namespace
+
+int main() {
+  StubRenderer renderer;
+  Button button;
+  button.setGlyph("home");
+  button.setGlyphSize(21.0F);
+  button.setContentAlign(ButtonContentAlign::Center);
+  button.setPadding(4.0F);
+  button.setSize(32.0F, 32.0F);
+  button.layout(renderer);
+
+  const Glyph* glyph = button.glyph();
+  if (glyph == nullptr) {
+    std::println(stderr, "button_layout_test: glyph was not created");
+    return 1;
+  }
+
+  const float glyphCenterX = glyph->x() + glyph->width() * 0.5F;
+  const float glyphCenterY = glyph->y() + glyph->height() * 0.5F;
+  const float buttonCenterX = button.width() * 0.5F;
+  const float buttonCenterY = button.height() * 0.5F;
+
+  if (!near(glyphCenterX, buttonCenterX) || !near(glyphCenterY, buttonCenterY)) {
+    std::println(
+        stderr, "button_layout_test: centered glyph mismatch: glyph center=({}, {}), button center=({}, {})",
+        glyphCenterX, glyphCenterY, buttonCenterX, buttonCenterY
+    );
+    return 1;
+  }
+
+  if (!near(glyph->x(), 5.5F) || !near(glyph->y(), 5.5F)) {
+    std::println(
+        stderr, "button_layout_test: expected a 21px glyph in a 32px button at (5.5, 5.5), got ({}, {})", glyph->x(),
+        glyph->y()
+    );
+    return 1;
+  }
+
+  return 0;
+}