Selectable: add support for specifying text alignment on selectables (#2347)

Adds a style variable to Selectable that allows clients to specify the
text alignment within Selectables, adds a section in the demo to
demonstrate selectable text alignment, and a pair of sliders in the
style editor to change selectable alignment on the fly.

In terms of implementation, this one is extremely simple: Selectable was
already calling an API that supports text alignment, but had hard-coded
it to top-left. This changes that to just pass the style variable
straight through to RenderTextClipped. Backwards-compatibility is
preserved by defaulting the text_align parameter to (0, 0), i.e.,
top-left.

This also fixes a bug with selectable text rendering that caused
right-aligned text in a selectable to be clipped incorrectly, because
the wrong clipping rectangle was being used.

imgui.cpp

@@ -1109,6 +1109,7 @@ ImGuiStyle::ImGuiStyle()
     AntiAliasedLines        = true;             // Enable anti-aliasing on lines/borders. Disable if you are really short on CPU/GPU.
     AntiAliasedFill         = true;             // Enable anti-aliasing on filled shapes (rounded rectangles, circles, etc.)
     CurveTessellationTol    = 1.25f;            // Tessellation tolerance when using PathBezierCurveTo() without a specific number of segments. Decrease for highly tessellated curves (higher quality, more polygons), increase to reduce quality.
+    SelectableTextAlign     = ImVec2(0,0);      // Alignment of selectable text when button is larger than text.
 
     // Default theme
     ImGui::StyleColorsDark(this);
@@ -5816,6 +5817,7 @@ static const ImGuiStyleVarInfo GStyleVarInfo[] =
     { ImGuiDataType_Float, 1, (ImU32)IM_OFFSETOF(ImGuiStyle, GrabRounding) },        // ImGuiStyleVar_GrabRounding
     { ImGuiDataType_Float, 1, (ImU32)IM_OFFSETOF(ImGuiStyle, TabRounding) },         // ImGuiStyleVar_TabRounding
     { ImGuiDataType_Float, 2, (ImU32)IM_OFFSETOF(ImGuiStyle, ButtonTextAlign) },     // ImGuiStyleVar_ButtonTextAlign
+    { ImGuiDataType_Float, 2, (ImU32)IM_OFFSETOF(ImGuiStyle, SelectableTextAlign) }, // ImGuiStyleVar_SelectableTextAlign
 };
 
 static const ImGuiStyleVarInfo* GetStyleVarInfo(ImGuiStyleVar idx)

imgui.h

@@ -1082,6 +1082,7 @@ enum ImGuiStyleVar_
     ImGuiStyleVar_GrabRounding,        // float     GrabRounding
     ImGuiStyleVar_TabRounding,         // float     TabRounding
     ImGuiStyleVar_ButtonTextAlign,     // ImVec2    ButtonTextAlign
+    ImGuiStyleVar_SelectableTextAlign, // ImVec2    SelectableTextAlign
     ImGuiStyleVar_COUNT
 
     // Obsolete names (will be removed)
@@ -1263,6 +1264,7 @@ struct ImGuiStyle
     bool        AntiAliasedLines;           // Enable anti-aliasing on lines/borders. Disable if you are really tight on CPU/GPU.
     bool        AntiAliasedFill;            // Enable anti-aliasing on filled shapes (rounded rectangles, circles, etc.)
     float       CurveTessellationTol;       // Tessellation tolerance when using PathBezierCurveTo() without a specific number of segments. Decrease for highly tessellated curves (higher quality, more polygons), increase to reduce quality.
+    ImVec2      SelectableTextAlign;        // Alignment of selectable text when selectable is larger than text. Defaults to (0,0) for top-left alignment.
     ImVec4      Colors[ImGuiCol_COUNT];
 
     IMGUI_API ImGuiStyle();

imgui_demo.cpp

@@ -893,6 +893,25 @@ static void ShowDemoWindowWidgets()
             }
             ImGui::TreePop();
         }
+        if (ImGui::TreeNode("Alignment"))
+        {
+            static bool selected[3*3] = { true, false, true, false, true, false, true, false, true };
+            static char name[16];
+            for (int i = 0; i < 3; i++)
+            {
+                for (int j = 0; j < 3; j++)
+                {
+                    float x = (float) i / 2.f;
+                    float y = (float) j / 2.f;
+                    snprintf(name, IM_ARRAYSIZE(name), "(%.1f,%.1f)", x, y);
+                    ImGui::PushStyleVar(ImGuiStyleVar_SelectableTextAlign, ImVec2(x, y));
+                    ImGui::Selectable(name, &selected[3*i+j], 0, ImVec2(70,70));
+                    ImGui::PopStyleVar();
+                    if (j != 2) ImGui::SameLine();
+                }
+            }
+            ImGui::TreePop();
+        }
         ImGui::TreePop();
     }
 
@@ -2825,6 +2844,7 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
             ImGui::Text("Alignment");
             ImGui::SliderFloat2("WindowTitleAlign", (float*)&style.WindowTitleAlign, 0.0f, 1.0f, "%.2f");
             ImGui::SliderFloat2("ButtonTextAlign", (float*)&style.ButtonTextAlign, 0.0f, 1.0f, "%.2f"); ImGui::SameLine(); ShowHelpMarker("Alignment applies when a button is larger than its text content.");
+            ImGui::SliderFloat2("SelectableTextAlign", (float*)&style.SelectableTextAlign, 0.0f, 1.0f, "%.2f"); ImGui::SameLine(); ShowHelpMarker("Alignment applies when a selectable is larger than its text content.");
             ImGui::Text("Safe Area Padding"); ImGui::SameLine(); ShowHelpMarker("Adjust if you cannot see the edges of your screen (e.g. on a TV where scaling has not been configured).");
             ImGui::SliderFloat2("DisplaySafeAreaPadding", (float*)&style.DisplaySafeAreaPadding, 0.0f, 30.0f, "%.0f");
             ImGui::EndTabItem();

imgui_widgets.cpp

@@ -5100,7 +5100,7 @@ bool ImGui::Selectable(const char* label, bool selected, ImGuiSelectableFlags fl
     }
 
     if (flags & ImGuiSelectableFlags_Disabled) PushStyleColor(ImGuiCol_Text, g.Style.Colors[ImGuiCol_TextDisabled]);
-    RenderTextClipped(bb_inner.Min, bb.Max, label, NULL, &label_size, ImVec2(0.0f,0.0f));
+    RenderTextClipped(bb_inner.Min, bb_inner.Max, label, NULL, &label_size, style.SelectableTextAlign, &bb);
     if (flags & ImGuiSelectableFlags_Disabled) PopStyleColor();
 
     // Automatically close popups