Scrollbar: clicking above or below the grab scrolls by one page, holding mouse button repeats scrolling. (#7328, #150)

Remove absolute seeking entirely. Amend f02108085.

docs/CHANGELOG.txt

@@ -45,6 +45,8 @@ Other changes:
 
 - Windows: fixed altering FramePadding mid-frame not correctly affecting logic
   responsible for honoring io.ConfigWindowsMoveFromTitleBarOnly. (#7576, #899)
+- Scrollbar: made scrolling logic more standard: clicking above or below the
+  grab scrolls by one page, holding mouse button repeats scrolling. (#7328, #150)
 
 
 -----------------------------------------------------------------------

imgui_internal.h

@@ -472,7 +472,7 @@ template<typename T> static inline T ImSubClampOverflow(T a, T b, T mn, T mx)
 // - Misc maths helpers
 static inline ImVec2 ImMin(const ImVec2& lhs, const ImVec2& rhs)                { return ImVec2(lhs.x < rhs.x ? lhs.x : rhs.x, lhs.y < rhs.y ? lhs.y : rhs.y); }
 static inline ImVec2 ImMax(const ImVec2& lhs, const ImVec2& rhs)                { return ImVec2(lhs.x >= rhs.x ? lhs.x : rhs.x, lhs.y >= rhs.y ? lhs.y : rhs.y); }
-static inline ImVec2 ImClamp(const ImVec2& v, const ImVec2& mn, ImVec2 mx)      { return ImVec2((v.x < mn.x) ? mn.x : (v.x > mx.x) ? mx.x : v.x, (v.y < mn.y) ? mn.y : (v.y > mx.y) ? mx.y : v.y); }
+static inline ImVec2 ImClamp(const ImVec2& v, const ImVec2&mn, const ImVec2&mx) { return ImVec2((v.x < mn.x) ? mn.x : (v.x > mx.x) ? mx.x : v.x, (v.y < mn.y) ? mn.y : (v.y > mx.y) ? mx.y : v.y); }
 static inline ImVec2 ImLerp(const ImVec2& a, const ImVec2& b, float t)          { return ImVec2(a.x + (b.x - a.x) * t, a.y + (b.y - a.y) * t); }
 static inline ImVec2 ImLerp(const ImVec2& a, const ImVec2& b, const ImVec2& t)  { return ImVec2(a.x + (b.x - a.x) * t.x, a.y + (b.y - a.y) * t.y); }
 static inline ImVec4 ImLerp(const ImVec4& a, const ImVec4& b, float t)          { return ImVec4(a.x + (b.x - a.x) * t, a.y + (b.y - a.y) * t, a.z + (b.z - a.z) * t, a.w + (b.w - a.w) * t); }
@@ -2162,13 +2162,14 @@ struct ImGuiContext
     ImGuiComboPreviewData   ComboPreviewData;
     ImRect                  WindowResizeBorderExpectedRect;     // Expected border rect, switch to relative edit if moving
     bool                    WindowResizeRelativeMode;
+    short                   ScrollbarSeekMode;                  // 0: relative, -1/+1: prev/next page.
+    float                   ScrollbarClickDeltaToGrabCenter;    // Distance between mouse and center of grab box, normalized in parent space. Use storage?
     float                   SliderGrabClickOffset;
     float                   SliderCurrentAccum;                 // Accumulated slider delta when using navigation controls.
     bool                    SliderCurrentAccumDirty;            // Has the accumulated slider delta changed since last time we tried to apply it?
     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
-    float                   ScrollbarClickDeltaToGrabCenter;    // Distance between mouse and center of grab box, normalized in parent space. Use storage?
     float                   DisabledAlphaBackup;                // Backup for style.Alpha for BeginDisabled()
     short                   DisabledStackSize;
     short                   LockMarkEdited;
@@ -2376,13 +2377,14 @@ struct ImGuiContext
         ColorEditSavedHue = ColorEditSavedSat = 0.0f;
         ColorEditSavedColor = 0;
         WindowResizeRelativeMode = false;
+        ScrollbarSeekMode = 0;
+        ScrollbarClickDeltaToGrabCenter = 0.0f;
         SliderGrabClickOffset = 0.0f;
         SliderCurrentAccum = 0.0f;
         SliderCurrentAccumDirty = false;
         DragCurrentAccumDirty = false;
         DragCurrentAccum = 0.0f;
         DragSpeedDefaultRatio = 1.0f / 100.0f;
-        ScrollbarClickDeltaToGrabCenter = 0.0f;
         DisabledAlphaBackup = 0.0f;
         DisabledStackSize = 0;
         LockMarkEdited = 0;

imgui_widgets.cpp

@@ -916,10 +916,10 @@ void ImGui::Scrollbar(ImGuiAxis axis)
         if (!window->ScrollbarX)
             rounding_corners |= ImDrawFlags_RoundCornersBottomRight;
     }
-    float size_avail = window->InnerRect.Max[axis] - window->InnerRect.Min[axis];
+    float size_visible = window->InnerRect.Max[axis] - window->InnerRect.Min[axis];
     float size_contents = window->ContentSize[axis] + window->WindowPadding[axis] * 2.0f;
     ImS64 scroll = (ImS64)window->Scroll[axis];
-    ScrollbarEx(bb, id, axis, &scroll, (ImS64)size_avail, (ImS64)size_contents, rounding_corners);
+    ScrollbarEx(bb, id, axis, &scroll, (ImS64)size_visible, (ImS64)size_contents, rounding_corners);
     window->Scroll[axis] = (float)scroll;
 }
 
@@ -929,7 +929,7 @@ void ImGui::Scrollbar(ImGuiAxis axis)
 // - 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.
 // Still, the code should probably be made simpler..
-bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, ImS64* p_scroll_v, ImS64 size_avail_v, ImS64 size_contents_v, ImDrawFlags flags)
+bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, ImS64* p_scroll_v, ImS64 size_visible_v, ImS64 size_contents_v, ImDrawFlags flags)
 {
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = g.CurrentWindow;
@@ -959,9 +959,9 @@ bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, ImS6
 
     // 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(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 ImS64 win_size_v = ImMax(ImMax(size_contents_v, size_avail_v), (ImS64)1);
-    const float grab_h_pixels = ImClamp(scrollbar_size_v * ((float)size_avail_v / (float)win_size_v), style.GrabMinSize, scrollbar_size_v);
+    IM_ASSERT(ImMax(size_contents_v, size_visible_v) > 0.0f); // Adding this assert to check if the ImMax(XXX,1.0f) is still needed. PLEASE CONTACT ME if this triggers.
+    const ImS64 win_size_v = ImMax(ImMax(size_contents_v, size_visible_v), (ImS64)1);
+    const float grab_h_pixels = ImClamp(scrollbar_size_v * ((float)size_visible_v / (float)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().
@@ -970,7 +970,7 @@ bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, ImS6
     ItemAdd(bb_frame, id, NULL, ImGuiItemFlags_NoNav);
     ButtonBehavior(bb, id, &hovered, &held, ImGuiButtonFlags_NoNavFocus);
 
-    const ImS64 scroll_max = ImMax((ImS64)1, size_contents_v - size_avail_v);
+    const ImS64 scroll_max = ImMax((ImS64)1, size_contents_v - size_visible_v);
     float scroll_ratio = ImSaturate((float)*p_scroll_v / (float)scroll_max);
     float grab_v_norm = scroll_ratio * (scrollbar_size_v - grab_h_pixels) / scrollbar_size_v; // Grab position in normalized space
     if (held && allow_interaction && grab_h_norm < 1.0f)
@@ -981,29 +981,39 @@ bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, ImS6
         // 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);
 
-        bool seek_absolute = false;
+        const int held_dir = (clicked_v_norm < grab_v_norm) ? -1 : (clicked_v_norm > grab_v_norm + grab_h_norm) ? +1 : 0;
         if (g.ActiveIdIsJustActivated)
         {
             // On initial click calculate the distance between mouse and the center of the grab
-            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
-                g.ScrollbarClickDeltaToGrabCenter = clicked_v_norm - grab_v_norm - grab_h_norm * 0.5f;
+            g.ScrollbarSeekMode = (short)held_dir;
+            g.ScrollbarClickDeltaToGrabCenter = (g.ScrollbarSeekMode == 0.0f) ? clicked_v_norm - grab_v_norm - grab_h_norm * 0.5f : 0.0f;
         }
 
         // Apply scroll (p_scroll_v will generally point on one member of window->Scroll)
         // It is ok to modify Scroll here because we are being called in Begin() after the calculation of ContentSize and before setting up our starting position
-        const float scroll_v_norm = ImSaturate((clicked_v_norm - g.ScrollbarClickDeltaToGrabCenter - grab_h_norm * 0.5f) / (1.0f - grab_h_norm));
-        *p_scroll_v = (ImS64)(scroll_v_norm * scroll_max);
+        if (g.ScrollbarSeekMode == 0)
+        {
+            // Absolute seeking
+            const float scroll_v_norm = ImSaturate((clicked_v_norm - g.ScrollbarClickDeltaToGrabCenter - grab_h_norm * 0.5f) / (1.0f - grab_h_norm));
+            *p_scroll_v = (ImS64)(scroll_v_norm * scroll_max);
+        }
+        else
+        {
+            // Page by page
+            if (IsMouseClicked(ImGuiMouseButton_Left, ImGuiInputFlags_Repeat) && held_dir == g.ScrollbarSeekMode)
+            {
+                float page_dir = (g.ScrollbarSeekMode > 0.0f) ? +1.0f : -1.0f;
+                *p_scroll_v = ImClamp(*p_scroll_v + (ImS64)(page_dir * size_visible_v), (ImS64)0, scroll_max);
+            }
+        }
 
         // Update values for rendering
         scroll_ratio = ImSaturate((float)*p_scroll_v / (float)scroll_max);
         grab_v_norm = scroll_ratio * (scrollbar_size_v - grab_h_pixels) / scrollbar_size_v;
 
         // Update distance to grab now that we have seek'ed and saturated
-        if (seek_absolute)
-            g.ScrollbarClickDeltaToGrabCenter = clicked_v_norm - grab_v_norm - grab_h_norm * 0.5f;
+        //if (seek_absolute)
+        //    g.ScrollbarClickDeltaToGrabCenter = clicked_v_norm - grab_v_norm - grab_h_norm * 0.5f;
     }
 
     // Render