Internal: Scrollbar: Extracted scrollbar code for other uses (eg. table v2 scrolling without using a child window).

imgui_internal.h

@@ -956,7 +956,7 @@ struct ImGuiContext
     bool                    DragCurrentAccumDirty;
     float                   DragCurrentAccum;                   // Accumulator for dragging modification. Always high-precision, not rounded by end-user precision settings
     float                   DragSpeedDefaultRatio;              // If speed == 0.0f, uses (max-min) * DragSpeedDefaultRatio
-    ImVec2                  ScrollbarClickDeltaToGrabCenter;    // Distance between mouse and center of grab box, normalized in parent space. Use storage?
+    float                   ScrollbarClickDeltaToGrabCenter;    // Distance between mouse and center of grab box, normalized in parent space. Use storage?
     int                     TooltipOverrideCount;
     ImVector<char>          PrivateClipboard;                   // If no custom clipboard handler is defined
 
@@ -1092,7 +1092,7 @@ struct ImGuiContext
         DragCurrentAccumDirty = false;
         DragCurrentAccum = 0.0f;
         DragSpeedDefaultRatio = 1.0f / 100.0f;
-        ScrollbarClickDeltaToGrabCenter = ImVec2(0.0f, 0.0f);
+        ScrollbarClickDeltaToGrabCenter = 0.0f;
         TooltipOverrideCount = 0;
 
         MultiSelectScopeId = 0;
@@ -1551,6 +1551,7 @@ namespace ImGui
     IMGUI_API bool          CollapseButton(ImGuiID id, const ImVec2& pos);
     IMGUI_API bool          ArrowButtonEx(const char* str_id, ImGuiDir dir, ImVec2 size_arg, ImGuiButtonFlags flags);
     IMGUI_API void          Scrollbar(ImGuiAxis axis);
+    IMGUI_API bool          ScrollbarEx(const ImRect& bb, ImGuiID id, ImGuiAxis axis, float* p_scroll_v, float avail_v, float contents_v, ImDrawCornerFlags rounding_corners);
     IMGUI_API ImGuiID       GetScrollbarID(ImGuiWindow* window, ImGuiAxis axis);
     IMGUI_API void          SeparatorEx(ImGuiSeparatorFlags flags);
 

imgui_widgets.cpp

@@ -380,6 +380,7 @@ void ImGui::BulletTextV(const char* fmt, va_list args)
 // - ArrowButton()
 // - CloseButton() [Internal]
 // - CollapseButton() [Internal]
+// - ScrollbarEx() [Internal]
 // - Scrollbar() [Internal]
 // - Image()
 // - ImageButton()
@@ -777,125 +778,133 @@ ImGuiID ImGui::GetScrollbarID(ImGuiWindow* window, ImGuiAxis axis)
 // - We handle absolute seeking (when first clicking outside the grab) and relative manipulation (afterward or when clicking inside the grab)
 // - We store values as normalized ratio and in a form that allows the window content to change while we are holding on a scrollbar
 // - We handle both horizontal and vertical scrollbars, which makes the terminology not ideal.
-void ImGui::Scrollbar(ImGuiAxis axis)
+// Still, the code should probably be made simpler..
+bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, float* p_scroll_v, float size_avail_v, float size_contents_v, ImDrawCornerFlags rounding_corners)
 {
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = g.CurrentWindow;
+    if (window->SkipItems)
+        return false;
 
-    const bool horizontal = (axis == ImGuiAxis_X);
-    const ImGuiStyle& style = g.Style;
-    const ImGuiID id = GetScrollbarID(window, axis);
-    KeepAliveID(id);
-
-    // Render background
-    bool other_scrollbar = (horizontal ? window->ScrollbarY : window->ScrollbarX);
-    float other_scrollbar_size_w = other_scrollbar ? style.ScrollbarSize : 0.0f;
-    const ImRect host_rect = window->Rect();
-    const float border_size = window->WindowBorderSize;
-    ImRect bb = horizontal
-        ? ImRect(host_rect.Min.x + border_size, host_rect.Max.y - style.ScrollbarSize, host_rect.Max.x - other_scrollbar_size_w - border_size, host_rect.Max.y - border_size)
-        : ImRect(host_rect.Max.x - style.ScrollbarSize, host_rect.Min.y + border_size, host_rect.Max.x - border_size, host_rect.Max.y - other_scrollbar_size_w - border_size);
-    bb.Min.x = ImMax(host_rect.Min.x, bb.Min.x); // Handle case where the host rectangle is smaller than the scrollbar
-    bb.Min.y = ImMax(host_rect.Min.y, bb.Min.y);
-    if (!horizontal)
-        bb.Min.y += window->TitleBarHeight() + ((window->Flags & ImGuiWindowFlags_MenuBar) ? window->MenuBarHeight() : 0.0f); // FIXME: InnerRect?
-
-    const float bb_width = bb.GetWidth();
-    const float bb_height = bb.GetHeight();
-    if (bb_width <= 0.0f || bb_height <= 0.0f)
-        return;
+    const float bb_frame_width = bb_frame.GetWidth();
+    const float bb_frame_height = bb_frame.GetHeight();
+    if (bb_frame_width <= 0.0f || bb_frame_height <= 0.0f)
+        return false;
 
     // When we are too small, start hiding and disabling the grab (this reduce visual noise on very small window and facilitate using the resize grab)
     float alpha = 1.0f;
-    if ((axis == ImGuiAxis_Y) && bb_height < g.FontSize + g.Style.FramePadding.y * 2.0f)
-    {
-        alpha = ImSaturate((bb_height - g.FontSize) / (g.Style.FramePadding.y * 2.0f));
-        if (alpha <= 0.0f)
-            return;
-    }
+    if ((axis == ImGuiAxis_Y) && bb_frame_height < g.FontSize + g.Style.FramePadding.y * 2.0f)
+        alpha = ImSaturate((bb_frame_height - g.FontSize) / (g.Style.FramePadding.y * 2.0f));
+    if (alpha <= 0.0f)
+        return false;
+
+    const ImGuiStyle& style = g.Style;
     const bool allow_interaction = (alpha >= 1.0f);
+    const bool horizontal = (axis == ImGuiAxis_X);
 
-    int window_rounding_corners;
-    if (horizontal)
-        window_rounding_corners = ImDrawCornerFlags_BotLeft | (other_scrollbar ? 0 : ImDrawCornerFlags_BotRight);
-    else
-        window_rounding_corners = (((window->Flags & ImGuiWindowFlags_NoTitleBar) && !(window->Flags & ImGuiWindowFlags_MenuBar)) ? ImDrawCornerFlags_TopRight : 0) | (other_scrollbar ? 0 : ImDrawCornerFlags_BotRight);
-    window->DrawList->AddRectFilled(bb.Min, bb.Max, GetColorU32(ImGuiCol_ScrollbarBg), window->WindowRounding, window_rounding_corners);
-    bb.Expand(ImVec2(-ImClamp((float)(int)((bb_width - 2.0f) * 0.5f), 0.0f, 3.0f), -ImClamp((float)(int)((bb_height - 2.0f) * 0.5f), 0.0f, 3.0f)));
+    ImRect bb = bb_frame;
+    bb.Expand(ImVec2(-ImClamp((float)(int)((bb_frame_width - 2.0f) * 0.5f), 0.0f, 3.0f), -ImClamp((float)(int)((bb_frame_height - 2.0f) * 0.5f), 0.0f, 3.0f)));
 
     // V denote the main, longer axis of the scrollbar (= height for a vertical scrollbar)
-    float scrollbar_size_v = horizontal ? bb.GetWidth() : bb.GetHeight();
-    float scroll_v = horizontal ? window->Scroll.x : window->Scroll.y;
-    float win_size_avail_v = (horizontal ? window->SizeFull.x : window->SizeFull.y) - other_scrollbar_size_w;
-    float win_size_contents_v = horizontal ? window->SizeContents.x : window->SizeContents.y;
+    const float scrollbar_size_v = horizontal ? bb.GetWidth() : bb.GetHeight();
 
     // Calculate the height of our grabbable box. It generally represent the amount visible (vs the total scrollable amount)
     // But we maintain a minimum size in pixel to allow for the user to still aim inside.
-    IM_ASSERT(ImMax(win_size_contents_v, win_size_avail_v) > 0.0f); // Adding this assert to check if the ImMax(XXX,1.0f) is still needed. PLEASE CONTACT ME if this triggers.
-    const float win_size_v = ImMax(ImMax(win_size_contents_v, win_size_avail_v), 1.0f);
-    const float grab_h_pixels = ImClamp(scrollbar_size_v * (win_size_avail_v / win_size_v), style.GrabMinSize, scrollbar_size_v);
+    IM_ASSERT(ImMax(size_contents_v, size_avail_v) > 0.0f); // Adding this assert to check if the ImMax(XXX,1.0f) is still needed. PLEASE CONTACT ME if this triggers.
+    const float win_size_v = ImMax(ImMax(size_contents_v, size_avail_v), 1.0f);
+    const float grab_h_pixels = ImClamp(scrollbar_size_v * (size_avail_v / win_size_v), style.GrabMinSize, scrollbar_size_v);
     const float grab_h_norm = grab_h_pixels / scrollbar_size_v;
 
     // Handle input right away. None of the code of Begin() is relying on scrolling position before calling Scrollbar().
     bool held = false;
     bool hovered = false;
-    const bool previously_held = (g.ActiveId == id);
     ButtonBehavior(bb, id, &hovered, &held, ImGuiButtonFlags_NoNavFocus);
 
-    float scroll_max = ImMax(1.0f, win_size_contents_v - win_size_avail_v);
-    float scroll_ratio = ImSaturate(scroll_v / scroll_max);
+    float scroll_max = ImMax(1.0f, size_contents_v - size_avail_v);
+    float scroll_ratio = ImSaturate(*p_scroll_v / scroll_max);
     float grab_v_norm = scroll_ratio * (scrollbar_size_v - grab_h_pixels) / scrollbar_size_v;
     if (held && allow_interaction && grab_h_norm < 1.0f)
     {
         float scrollbar_pos_v = horizontal ? bb.Min.x : bb.Min.y;
         float mouse_pos_v = horizontal ? g.IO.MousePos.x : g.IO.MousePos.y;
-        float* click_delta_to_grab_center_v = horizontal ? &g.ScrollbarClickDeltaToGrabCenter.x : &g.ScrollbarClickDeltaToGrabCenter.y;
 
         // Click position in scrollbar normalized space (0.0f->1.0f)
         const float clicked_v_norm = ImSaturate((mouse_pos_v - scrollbar_pos_v) / scrollbar_size_v);
         SetHoveredID(id);
 
         bool seek_absolute = false;
-        if (!previously_held)
+        if (g.ActiveIdIsJustActivated)
         {
             // On initial click calculate the distance between mouse and the center of the grab
-            if (clicked_v_norm >= grab_v_norm && clicked_v_norm <= grab_v_norm + grab_h_norm)
-            {
-                *click_delta_to_grab_center_v = clicked_v_norm - grab_v_norm - grab_h_norm*0.5f;
-            }
+            seek_absolute = (clicked_v_norm < grab_v_norm || clicked_v_norm > grab_v_norm + grab_h_norm);
+            if (seek_absolute)
+                g.ScrollbarClickDeltaToGrabCenter = 0.0f;
             else
-            {
-                seek_absolute = true;
-                *click_delta_to_grab_center_v = 0.0f;
-            }
+                g.ScrollbarClickDeltaToGrabCenter = clicked_v_norm - grab_v_norm - grab_h_norm * 0.5f;
         }
 
         // Apply scroll
         // It is ok to modify Scroll here because we are being called in Begin() after the calculation of SizeContents and before setting up our starting position
-        const float scroll_v_norm = ImSaturate((clicked_v_norm - *click_delta_to_grab_center_v - grab_h_norm*0.5f) / (1.0f - grab_h_norm));
-        scroll_v = (float)(int)(0.5f + scroll_v_norm * scroll_max);//(win_size_contents_v - win_size_v));
-        if (horizontal)
-            window->Scroll.x = scroll_v;
-        else
-            window->Scroll.y = scroll_v;
+        const float scroll_v_norm = ImSaturate((clicked_v_norm - g.ScrollbarClickDeltaToGrabCenter - grab_h_norm * 0.5f) / (1.0f - grab_h_norm));
+        *p_scroll_v = (float)(int)(0.5f + scroll_v_norm * scroll_max);//(win_size_contents_v - win_size_v));
 
         // Update values for rendering
-        scroll_ratio = ImSaturate(scroll_v / scroll_max);
+        scroll_ratio = ImSaturate(*p_scroll_v / scroll_max);
         grab_v_norm = scroll_ratio * (scrollbar_size_v - grab_h_pixels) / scrollbar_size_v;
 
         // Update distance to grab now that we have seeked and saturated
         if (seek_absolute)
-            *click_delta_to_grab_center_v = clicked_v_norm - grab_v_norm - grab_h_norm*0.5f;
+            g.ScrollbarClickDeltaToGrabCenter = clicked_v_norm - grab_v_norm - grab_h_norm * 0.5f;
     }
 
-    // Render grab
+    // Render
+    window->DrawList->AddRectFilled(bb_frame.Min, bb_frame.Max, GetColorU32(ImGuiCol_ScrollbarBg), window->WindowRounding, rounding_corners);
     const ImU32 grab_col = GetColorU32(held ? ImGuiCol_ScrollbarGrabActive : hovered ? ImGuiCol_ScrollbarGrabHovered : ImGuiCol_ScrollbarGrab, alpha);
     ImRect grab_rect;
     if (horizontal)
-        grab_rect = ImRect(ImLerp(bb.Min.x, bb.Max.x, grab_v_norm), bb.Min.y, ImMin(ImLerp(bb.Min.x, bb.Max.x, grab_v_norm) + grab_h_pixels, host_rect.Max.x), bb.Max.y);
+        grab_rect = ImRect(ImLerp(bb.Min.x, bb.Max.x, grab_v_norm), bb.Min.y, ImLerp(bb.Min.x, bb.Max.x, grab_v_norm) + grab_h_pixels, bb.Max.y);
     else
-        grab_rect = ImRect(bb.Min.x, ImLerp(bb.Min.y, bb.Max.y, grab_v_norm), bb.Max.x, ImMin(ImLerp(bb.Min.y, bb.Max.y, grab_v_norm) + grab_h_pixels, host_rect.Max.y));
+        grab_rect = ImRect(bb.Min.x, ImLerp(bb.Min.y, bb.Max.y, grab_v_norm), bb.Max.x, ImLerp(bb.Min.y, bb.Max.y, grab_v_norm) + grab_h_pixels);
     window->DrawList->AddRectFilled(grab_rect.Min, grab_rect.Max, grab_col, style.ScrollbarRounding);
+
+    return held;
+}
+
+void ImGui::Scrollbar(ImGuiAxis axis)
+{
+    ImGuiContext& g = *GImGui;
+    ImGuiWindow* window = g.CurrentWindow;
+
+    const bool horizontal = (axis == ImGuiAxis_X);
+    const ImGuiStyle& style = g.Style;
+    const ImGuiID id = GetScrollbarID(window, axis);
+    KeepAliveID(id);
+
+    // Calculate our bounding box (FIXME: This is messy, should be made simpler using e.g. InnerRect/WorkRect data).
+    const float other_scrollbar_size = window->ScrollbarSizes[axis];
+    const ImRect win_rect = window->Rect();
+    const float border_size = window->WindowBorderSize;
+    ImRect bb = horizontal
+        ? ImRect(win_rect.Min.x + border_size, win_rect.Max.y - style.ScrollbarSize, win_rect.Max.x - other_scrollbar_size - border_size, win_rect.Max.y - border_size)
+        : ImRect(win_rect.Max.x - style.ScrollbarSize, win_rect.Min.y + border_size, win_rect.Max.x - border_size, win_rect.Max.y - other_scrollbar_size - border_size);
+    bb.Min.x = ImMax(win_rect.Min.x, bb.Min.x); // Handle case where the host rectangle is smaller than the scrollbar
+    bb.Min.y = ImMax(win_rect.Min.y, bb.Min.y);
+    if (!horizontal)
+        bb.Min.y += window->TitleBarHeight() + ((window->Flags & ImGuiWindowFlags_MenuBar) ? window->MenuBarHeight() : 0.0f); // FIXME: InnerRect?
+
+    // Select rounding
+    ImDrawCornerFlags rounding_corners;
+    if (horizontal)
+        rounding_corners = ImDrawCornerFlags_BotLeft;
+    else
+        rounding_corners = ((window->Flags & ImGuiWindowFlags_NoTitleBar) && !(window->Flags & ImGuiWindowFlags_MenuBar)) ? ImDrawCornerFlags_TopRight : 0;
+    if (other_scrollbar_size <= 0.0f)
+        rounding_corners |= ImDrawCornerFlags_BotRight;
+
+    if (horizontal)
+        ScrollbarEx(bb, id, axis, &window->Scroll.x, window->SizeFull.x - other_scrollbar_size, window->SizeContents.x, rounding_corners);
+    else
+        ScrollbarEx(bb, id, axis, &window->Scroll.y, window->SizeFull.y - other_scrollbar_size, window->SizeContents.y, rounding_corners);
 }
 
 void ImGui::Image(ImTextureID user_texture_id, const ImVec2& size, const ImVec2& uv0, const ImVec2& uv1, const ImVec4& tint_col, const ImVec4& border_col)