ColorButton: Reduced bordering artefact that would be particularly visible with opaque Col_FrameBg and FrameRounding enabled.

imgui.cpp

@@ -9281,15 +9281,18 @@ bool ImGui::ColorButton(const char* desc_id, const ImVec4& col, ImGuiColorEditFl
     ImVec4 col_without_alpha(col.x, col.y, col.z, 1.0f);
     float grid_step = ImMin(size.x, size.y) / 2.99f;
     float rounding = ImMin(g.Style.FrameRounding, grid_step * 0.5f);
+    ImRect bb_inner = bb;
+    float off = -0.75f; // The border (using Col_FrameBg) tends to look off when color is near-opaque and rounding is enabled. This offset seemed like a good middleground to reduce those artefacts.
+    bb_inner.Expand(off);
     if ((flags & ImGuiColorEditFlags_AlphaPreviewHalf) && col.w < 1.0f)
     {
-        float mid_x = (float)(int)((bb.Min.x + bb.Max.x) * 0.5f + 0.5f);
-        RenderColorRectWithAlphaCheckerboard(ImVec2(bb.Min.x + grid_step, bb.Min.y), bb.Max, GetColorU32(col), grid_step, ImVec2(-grid_step, 0.0f), rounding, ImGuiCorner_TopRight|ImGuiCorner_BotRight);
-        window->DrawList->AddRectFilled(bb.Min, ImVec2(mid_x, bb.Max.y), GetColorU32(col_without_alpha), rounding, ImGuiCorner_TopLeft|ImGuiCorner_BotLeft);
+        float mid_x = (float)(int)((bb_inner.Min.x + bb_inner.Max.x) * 0.5f + 0.5f);
+        RenderColorRectWithAlphaCheckerboard(ImVec2(bb_inner.Min.x + grid_step, bb_inner.Min.y), bb_inner.Max, GetColorU32(col), grid_step, ImVec2(-grid_step + off, off), rounding, ImGuiCorner_TopRight|ImGuiCorner_BotRight);
+        window->DrawList->AddRectFilled(bb_inner.Min, ImVec2(mid_x, bb_inner.Max.y), GetColorU32(col_without_alpha), rounding, ImGuiCorner_TopLeft|ImGuiCorner_BotLeft);
     }
     else
     {
-        RenderColorRectWithAlphaCheckerboard(bb.Min, bb.Max, GetColorU32((flags & ImGuiColorEditFlags_AlphaPreview) ? col : col_without_alpha), grid_step, ImVec2(0,0), rounding);
+        RenderColorRectWithAlphaCheckerboard(bb_inner.Min, bb_inner.Max, GetColorU32((flags & ImGuiColorEditFlags_AlphaPreview) ? col : col_without_alpha), grid_step, ImVec2(off, off), rounding);
     }
     if (window->Flags & ImGuiWindowFlags_ShowBorders)
         RenderFrameBorder(bb.Min, bb.Max, rounding);