Added SetScrollXHere, SetScrollFromPosX: Changelog, demo, comments (#1580).

docs/CHANGELOG.txt

@@ -45,6 +45,7 @@ Other Changes:
 - Window: Fixed InnerClipRect right-most coordinates using wrong padding setting (introduced in 1.71).
 - Word-wrapping: Fixed overzealous word-wrapping when glyph edge lands exactly on the limit. Because
   of this, auto-fitting exactly unwrapped text would make it wrap. (fixes initial 1.15 commit, 78645a7d).
+- Scrolling: Added SetScrollHereX(), SetScrollFromPosX() for completeness. (#1580) [@kevreco]
 - Style: Attenuated default opacity of ImGuiCol_Separator in Classic and Light styles.
 - ImDrawList: Fixed CloneOutput() helper crashing. (#1860) [@gviot]
 - ImDrawList::ChannelsSplit(), ImDrawListSplitter: Fixed an issue with merging draw commands between

docs/TODO.txt

@@ -30,6 +30,7 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - window/opt: freeze window flag: if not focused/hovered, return false, render with previous ImDrawList. and/or reduce refresh rate. -> this may require enforcing that it is illegal to submit contents if Begin returns false.
  - window/child: the first draw command of a child window could be moved into the current draw command of the parent window (unless child+tooltip?).
  - window/child: border could be emitted in parent as well.
+ - window/child: allow SetNextWindowContentSize() to work on child windows.
  - window/clipping: some form of clipping when DisplaySize (or corresponding viewport) is zero.
  - window/tab: add a way to signify that a window or docked window requires attention (e.g. blinking title bar).
  - scrolling: while holding down a scrollbar, try to keep the same contents visible (at least while not moving mouse)

imgui.cpp

@@ -6857,22 +6857,22 @@ void ImGui::SetScrollY(float scroll_y)
     window->ScrollTargetCenterRatio.y = 0.0f;
 }
 
-void ImGui::SetScrollFromPosY(float local_y, float center_y_ratio)
+void ImGui::SetScrollFromPosX(float local_x, float center_x_ratio)
 {
     // We store a target position so centering can occur on the next frame when we are guaranteed to have a known window size
     ImGuiWindow* window = GetCurrentWindow();
-    IM_ASSERT(center_y_ratio >= 0.0f && center_y_ratio <= 1.0f);
+    IM_ASSERT(center_x_ratio >= 0.0f && center_x_ratio <= 1.0f);
-    window->ScrollTarget.y = (float)(int)(local_y + window->Scroll.y);
+    window->ScrollTarget.x = (float)(int)(local_x + window->Scroll.x);
-    window->ScrollTargetCenterRatio.y = center_y_ratio;
+    window->ScrollTargetCenterRatio.x = center_x_ratio;
 }
 
-void ImGui::SetScrollFromPosX(float local_x, float center_x_ratio)
+void ImGui::SetScrollFromPosY(float local_y, float center_y_ratio)
 {
     // We store a target position so centering can occur on the next frame when we are guaranteed to have a known window size
     ImGuiWindow* window = GetCurrentWindow();
-    IM_ASSERT(center_x_ratio >= 0.0f && center_x_ratio <= 1.0f);
+    IM_ASSERT(center_y_ratio >= 0.0f && center_y_ratio <= 1.0f);
-    window->ScrollTarget.x = (float)(int)(local_x + window->Scroll.x);
+    window->ScrollTarget.y = (float)(int)(local_y + window->Scroll.y);
-    window->ScrollTargetCenterRatio.x = center_x_ratio;
+    window->ScrollTargetCenterRatio.y = center_y_ratio;
 }
 
 // center_x_ratio: 0.0f left of last item, 0.5f horizontal center of last item, 1.0f right of last item.

imgui_demo.cpp

@@ -1744,7 +1744,7 @@ static void ShowDemoWindowLayout()
         // - Using ImGui::GetItemRectMin/Max() to query the "item" state (because the child window is an item from the POV of the parent window)
         //   See "Widgets" -> "Querying Status (Active/Focused/Hovered etc.)" section for more details about this.
         {
-            ImGui::SetCursorPosX(50);
+            ImGui::SetCursorPosX(ImGui::GetCursorPosX() + 10);
             ImGui::PushStyleColor(ImGuiCol_ChildBg, IM_COL32(255, 0, 0, 100));
             ImGui::BeginChild("blah", ImVec2(200, 100), true, ImGuiWindowFlags_None);
             for (int n = 0; n < 50; n++)
@@ -1957,7 +1957,7 @@ static void ShowDemoWindowLayout()
 
     if (ImGui::TreeNode("Groups"))
     {
-        HelpMarker("Using ImGui::BeginGroup()/EndGroup() to layout items. BeginGroup() basically locks the horizontal position. EndGroup() bundles the whole group so that you can use functions such as IsItemHovered() on it.");
+        HelpMarker("BeginGroup() basically locks the horizontal position for new line. EndGroup() bundles the whole group so that you can use \"item\" functions such as IsItemHovered()/IsItemActive() or SameLine() etc. on the whole group.");
         ImGui::BeginGroup();
         {
             ImGui::BeginGroup();
@@ -2056,21 +2056,22 @@ static void ShowDemoWindowLayout()
 
     if (ImGui::TreeNode("Scrolling"))
     {
-        HelpMarker("Use SetScrollHereY() or SetScrollFromPosY() to scroll to a given position.");
+        // Vertical scroll functions
+        HelpMarker("Use SetScrollHereY() or SetScrollFromPosY() to scroll to a given vertical position.");
 
         static bool track = true;
-        static int track_line = 50;
+        static int track_item = 50;
         static float scroll_to_off_px = 0.0f;
         static float scroll_to_pos_px = 200.0f;
         ImGui::Checkbox("Track", &track);
         ImGui::PushItemWidth(100);
-        ImGui::SameLine(140); track |= ImGui::DragInt("##line", &track_line, 0.25f, 0, 99, "Line = %d");
+        ImGui::SameLine(140); track |= ImGui::DragInt("##item", &track_item, 0.25f, 0, 99, "Item = %d");
 
         bool scroll_to_off = ImGui::Button("Scroll Offset");
-        ImGui::SameLine(140); scroll_to_off |= ImGui::DragFloat("##off_y", &scroll_to_off_px, 1.00f, 0, 9999, "+%.0f px");
+        ImGui::SameLine(140); scroll_to_off |= ImGui::DragFloat("##off", &scroll_to_off_px, 1.00f, 0, 9999, "+%.0f px");
 
         bool scroll_to_pos = ImGui::Button("Scroll To Pos");
-        ImGui::SameLine(140); scroll_to_pos |= ImGui::DragFloat("##pos_y", &scroll_to_pos_px, 1.00f, 0, 9999, "Y = %.0f px");
+        ImGui::SameLine(140); scroll_to_pos |= ImGui::DragFloat("##pos", &scroll_to_pos_px, 1.00f, 0, 9999, "X/Y = %.0f px");
 
         ImGui::PopItemWidth();
         if (scroll_to_off || scroll_to_pos)
@@ -2078,28 +2079,31 @@ static void ShowDemoWindowLayout()
 
         ImGuiStyle& style = ImGui::GetStyle();
         float child_w = (ImGui::GetContentRegionAvail().x - 4 * style.ItemSpacing.x) / 5;
+        if (child_w < 20.0f)
+            child_w = 20.0f;
+        ImGui::PushID("##VerticalScrolling");
         for (int i = 0; i < 5; i++)
         {
             if (i > 0) ImGui::SameLine();
             ImGui::BeginGroup();
-            ImGui::Text("%s", i == 0 ? "Top" : i == 1 ? "25%" : i == 2 ? "Center" : i == 3 ? "75%" : "Bottom");
+            const char* names[] = { "Top", "25%", "Center", "75%", "Bottom" };
+            ImGui::TextUnformatted(names[i]);
 
-            ImGuiWindowFlags child_flags = ImGuiWindowFlags_MenuBar;
+            ImGui::BeginChild(ImGui::GetID((void*)(intptr_t)i), ImVec2(child_w, 200.0f), true, ImGuiWindowFlags_None);
-            ImGui::BeginChild(ImGui::GetID((void*)(intptr_t)i), ImVec2(child_w, 200.0f), true, child_flags);
             if (scroll_to_off)
                 ImGui::SetScrollY(scroll_to_off_px);
             if (scroll_to_pos)
                 ImGui::SetScrollFromPosY(ImGui::GetCursorStartPos().y + scroll_to_pos_px, i * 0.25f);
-            for (int line = 0; line < 100; line++)
+            for (int item = 0; item < 100; item++)
             {
-                if (track && line == track_line)
+                if (track && item == track_item)
                 {
-                    ImGui::TextColored(ImVec4(1,1,0,1), "Line %d", line);
+                    ImGui::TextColored(ImVec4(1,1,0,1), "Item %d", item);
                     ImGui::SetScrollHereY(i * 0.25f); // 0.0f:top, 0.5f:center, 1.0f:bottom
                 }
                 else
                 {
-                    ImGui::Text("Line %d", line);
+                    ImGui::Text("Item %d", item);
                 }
             }
             float scroll_y = ImGui::GetScrollY();
@@ -2108,11 +2112,44 @@ static void ShowDemoWindowLayout()
             ImGui::Text("%.0f/%.0f", scroll_y, scroll_max_y);
             ImGui::EndGroup();
         }
-        ImGui::TreePop();
+        ImGui::PopID();
-    }
 
-    if (ImGui::TreeNode("Horizontal Scrolling"))
+        // Horizontal scroll functions
+        ImGui::Spacing();
+        HelpMarker("Use SetScrollHereX() or SetScrollFromPosX() to scroll to a given horizontal position.\n\nUsing the \"Scroll To Pos\" button above will make the discontinuity at edges visible: scrolling to the top/bottom/left/right-most item will add an additional WindowPadding to reflect on reaching the edge of the list.\n\nBecause the clipping rectangle of most window hides half worth of WindowPadding on the left/right, using SetScrollFromPosX(+1) will usually result in clipped text whereas the equivalent SetScrollFromPosY(+1) wouldn't.");
+        ImGui::PushID("##HorizontalScrolling");
+        for (int i = 0; i < 5; i++)
+        {
+            float child_height = ImGui::GetTextLineHeight() + style.ScrollbarSize + style.WindowPadding.y * 2.0f;
+            ImGui::BeginChild(ImGui::GetID((void*)(intptr_t)i), ImVec2(-100, child_height), true, ImGuiWindowFlags_HorizontalScrollbar);
+            if (scroll_to_off)
+                ImGui::SetScrollX(scroll_to_off_px);
+            if (scroll_to_pos)
+                ImGui::SetScrollFromPosX(ImGui::GetCursorStartPos().x + scroll_to_pos_px, i * 0.25f);
+            for (int item = 0; item < 100; item++)
+            {
+                if (track && item == track_item)
+                {
+                    ImGui::TextColored(ImVec4(1, 1, 0, 1), "Item %d", item);
+                    ImGui::SetScrollHereX(i * 0.25f); // 0.0f:left, 0.5f:center, 1.0f:right
+                }
+                else
                 {
+                    ImGui::Text("Item %d", item);
+                }
+                ImGui::SameLine();
+            }
+            float scroll_x = ImGui::GetScrollX();
+            float scroll_max_x = ImGui::GetScrollMaxX();
+            ImGui::EndChild();
+            ImGui::SameLine();
+            const char* names[] = { "Left", "25%", "Center", "75%", "Right" };
+            ImGui::Text("%s\n%.0f/%.0f", names[i], scroll_x, scroll_max_x);
+            ImGui::Spacing();
+        }
+        ImGui::PopID();
+
+        // Miscellaneous Horizontal Scrolling Demo
         HelpMarker("Horizontal scrolling for a window has to be enabled explicitly via the ImGuiWindowFlags_HorizontalScrollbar flag.\n\nYou may want to explicitly specify content width by calling SetNextWindowContentWidth() before Begin().");
         static int lines = 7;
         ImGui::SliderInt("Lines", &lines, 1, 15);