ColorPicker4: hue/alpha bars draw arrows that would look right on all background. RenderArrow helper. (#346)

imgui.cpp

@@ -9329,6 +9329,26 @@ bool ImGui::ColorPicker3(const char* label, float col[3], ImGuiColorEditFlags fl
     return true;
 }
 
+// 'pos' is position of the arrow tip. half_sz.x is length from base to tip. half_sz.y is length on each side.
+static void RenderArrow(ImDrawList* draw_list, ImVec2 pos, ImVec2 half_sz, ImGuiDir direction, ImU32 col)
+{
+    switch (direction)
+    {
+    case ImGuiDir_Right: draw_list->AddTriangleFilled(ImVec2(pos.x - half_sz.x, pos.y + half_sz.y), ImVec2(pos.x - half_sz.x, pos.y - half_sz.y), pos, col); return;
+    case ImGuiDir_Left:  draw_list->AddTriangleFilled(ImVec2(pos.x + half_sz.x, pos.y - half_sz.y), ImVec2(pos.x + half_sz.x, pos.y + half_sz.y), pos, col); return;
+    case ImGuiDir_Down:  draw_list->AddTriangleFilled(ImVec2(pos.x - half_sz.x, pos.y - half_sz.y), ImVec2(pos.x + half_sz.x, pos.y - half_sz.y), pos, col); return;
+    case ImGuiDir_Up:    draw_list->AddTriangleFilled(ImVec2(pos.x + half_sz.x, pos.y + half_sz.y), ImVec2(pos.x - half_sz.x, pos.y + half_sz.y), pos, col); return;
+    }
+}
+
+static void RenderArrowsForVerticalBar(ImDrawList* draw_list, ImVec2 pos, ImVec2 half_sz, float bar_w)
+{
+    RenderArrow(draw_list, ImVec2(pos.x + half_sz.x + 1,         pos.y), ImVec2(half_sz.x + 2, half_sz.y + 1), ImGuiDir_Right, IM_COL32_BLACK);
+    RenderArrow(draw_list, ImVec2(pos.x + half_sz.x,             pos.y), half_sz,                              ImGuiDir_Right, IM_COL32_WHITE);
+    RenderArrow(draw_list, ImVec2(pos.x + bar_w - half_sz.x - 1, pos.y), ImVec2(half_sz.x + 2, half_sz.y + 1), ImGuiDir_Left,  IM_COL32_BLACK);
+    RenderArrow(draw_list, ImVec2(pos.x + bar_w - half_sz.x,     pos.y), half_sz,                              ImGuiDir_Left,  IM_COL32_WHITE);
+}
+
 // ColorPicker
 // Note: only access 3 floats if ImGuiColorEditFlags_NoAlpha flag is set.
 // FIXME: we adjust the big color square height based on item width, which may cause a flickering feedback loop (if automatic height makes a vertical scrollbar appears, affecting automatic width..) 
@@ -9351,10 +9371,10 @@ bool ImGui::ColorPicker4(const char* label, float col[4], ImGuiColorEditFlags fl
     bool alpha_bar = (flags & ImGuiColorEditFlags_AlphaBar) && !(flags & ImGuiColorEditFlags_NoAlpha);
     ImVec2 picker_pos = window->DC.CursorPos;
     float bars_width = ColorSquareSize(); // Arbitrary smallish width of Hue/Alpha picking bars
-    float bars_line_extrude = ImMin(2.0f, style.ItemInnerSpacing.x * 0.5f);
     float sv_picker_size = ImMax(bars_width * 1, CalcItemWidth() - (alpha_bar ? 2 : 1) * (bars_width + style.ItemInnerSpacing.x)); // Saturation/Value picking box
     float bar0_pos_x = picker_pos.x + sv_picker_size + style.ItemInnerSpacing.x;
     float bar1_pos_x = bar0_pos_x + bars_width + style.ItemInnerSpacing.x;
+    float bars_triangles_half_sz = (float)(int)(bars_width * 0.20f);
 
     float H,S,V;
     ColorConvertRGBtoHSV(col[0], col[1], col[2], H, S, V);
@@ -9476,17 +9496,17 @@ bool ImGui::ColorPicker4(const char* label, float col[4], ImGuiColorEditFlags fl
     }
     float bar0_line_y = (float)(int)(picker_pos.y + H * sv_picker_size + 0.5f);
     RenderFrameBorder(ImVec2(bar0_pos_x, picker_pos.y), ImVec2(bar0_pos_x + bars_width, picker_pos.y + sv_picker_size), 0.0f);
-    draw_list->AddLine(ImVec2(bar0_pos_x - bars_line_extrude, bar0_line_y), ImVec2(bar0_pos_x + bars_width + bars_line_extrude, bar0_line_y), IM_COL32_WHITE);
+    RenderArrowsForVerticalBar(draw_list, ImVec2(bar0_pos_x - 1, bar0_line_y), ImVec2(bars_triangles_half_sz + 1, bars_triangles_half_sz), bars_width + 2.0f);
 
     // Render alpha bar
     if (alpha_bar)
     {
         float alpha = ImSaturate(col[3]);
-        float bar1_line_y = (float)(int)(picker_pos.y + (1.0f - alpha) * sv_picker_size + 0.5f);
         ImRect bar1_bb(bar1_pos_x, picker_pos.y, bar1_pos_x + bars_width, picker_pos.y + sv_picker_size);
         draw_list->AddRectFilledMultiColor(bar1_bb.Min, bar1_bb.Max, IM_COL32_WHITE, IM_COL32_WHITE, IM_COL32_BLACK, IM_COL32_BLACK);
+        float bar1_line_y = (float)(int)(picker_pos.y + (1.0f - alpha) * sv_picker_size + 0.5f);
         RenderFrameBorder(bar1_bb.Min, bar1_bb.Max, 0.0f);
-        draw_list->AddLine(ImVec2(bar1_pos_x - bars_line_extrude, bar1_line_y), ImVec2(bar1_pos_x + bars_width + bars_line_extrude, bar1_line_y), IM_COL32_WHITE);
+        RenderArrowsForVerticalBar(draw_list, ImVec2(bar1_pos_x - 1, bar1_line_y), ImVec2(bars_triangles_half_sz + 1, bars_triangles_half_sz), bars_width + 2.0f);
     }
 
     // Render color matrix

imgui_demo.cpp

@@ -687,7 +687,7 @@ void ImGui::ShowTestWindow(bool* p_open)
 
             ImGui::Text("Color picker:");
             static bool alpha = true;
-            static bool alpha_bar = false;
+            static bool alpha_bar = true;
             static bool side_preview = true;
             static bool ref_color = false;
             static ImVec4 ref_color_v(1.0f,0.0f,1.0f,0.5f);

imgui_internal.h

@@ -202,6 +202,15 @@ enum ImGuiDataType
     ImGuiDataType_Float2,
 };
 
+enum ImGuiDir
+{
+    ImGuiDir_None    = -1,
+    ImGuiDir_Left    = 0,
+    ImGuiDir_Right   = 1,
+    ImGuiDir_Up      = 2,
+    ImGuiDir_Down    = 3,
+};
+
 enum ImGuiCorner
 {
     ImGuiCorner_TopLeft     = 1 << 0, // 1