Tables: simplified and tidying up TableSetColumnWidth(), fixes resizing a fixed column surrounded by stretch column (manually or via auto-fit menu). TableHeader() showing highlighted when held.

imgui.h

@@ -1050,7 +1050,7 @@ enum ImGuiTabItemFlags_
 //    - Using Stretch columns OFTEN DOES NOT MAKE SENSE if ScrollX is on, UNLESS you have specified a value for 'inner_width' in BeginTable().
 // - Mixing up columns with different sizing policy is possible BUT can be tricky and has some side-effects and restrictions.
 //   (their visible order and the scrolling state have subtle but necessary effects on how they can be manually resized).
-//   The typical use of mixing sizing policies is to have ScrollX disabled, one or two Stretch Column and many Fixed Columns.
+//   The typical use of mixing sizing policies is to have ScrollX disabled, first Fixed columns and then one or two TRAILING Stretch columns.
 enum ImGuiTableFlags_
 {
     // Features

imgui_tables.cpp

@@ -1876,6 +1876,7 @@ void ImGui::TableSetColumnWidth(int column_n, float width)
     if (column_0->WidthGiven == column_0_width || column_0->WidthRequest == column_0_width)
         return;
 
+    //IMGUI_DEBUG_LOG("TableSetColumnWidth(%d, %.1f->%.1f)\n", column_0_idx, column_0->WidthGiven, column_0_width);
     ImGuiTableColumn* column_1 = (column_0->NextEnabledColumn != -1) ? &table->Columns[column_0->NextEnabledColumn] : NULL;
 
     // In this surprisingly not simple because of how we support mixing Fixed and multiple Stretch columns.
@@ -1897,66 +1898,44 @@ void ImGui::TableSetColumnWidth(int column_n, float width)
     // - W1 F2 F3  resize from F3|          --> ok: no-op (disabled by Resize Rule 1)
     // - W1 F2     resize from F2|          --> ok: no-op (disabled by Resize Rule 1)
     // - W1 W2 F3  resize from W1| or W2|   --> ok
-    // - W1 F2 W3  resize from W1| or F2|   --> FIXME
+    // - W1 F2 W3  resize from W1| or F2|   --> ok
     // - F1 W2 F3  resize from W2|          --> ok
     // - F1 W3 F2  resize from W3|          --> ok
-    // - W1 F2 F3  resize from W1|          --> ok: equivalent to resizing |F2. F3 will not move. (forwarded by Resize Rule 2)
+    // - W1 F2 F3  resize from W1|          --> ok: equivalent to resizing |F2. F3 will not move.
     // - W1 F2 F3  resize from F2|          --> ok
     // All resizes from a Wx columns are locking other columns.
 
     // Possible improvements:
     // - W1 W2 W3  resize W1|               --> to not be stuck, both W2 and W3 would stretch down. Seems possible to fix. Would be most beneficial to simplify resize of all-weighted columns.
-    // - W1 F2 W3  resize W1| or F2|        --> symmetrical resize is weird and glitchy. Seems possible to fix.
     // - W3 F1 F2  resize W3|               --> to not be stuck past F1|, both F1 and F2 would need to stretch down, which would be lossy or ambiguous. Seems hard to fix.
 
-    // Rules:
-    // - [Resize Rule 1] Can't resize from right of right-most visible column if there is any Stretch column. Implemented in TableUpdateLayout().
-    // - [Resize Rule 2] Resizing from right-side of a Stretch column before a fixed column forward sizing to left-side of fixed column.
-    // - [Resize Rule 3] If we are are followed by a fixed column and we have a Stretch column before, we need to ensure that our left border won't move.
-    table->IsSettingsDirty = true;
-    if (column_0->Flags & ImGuiTableColumnFlags_WidthFixed)
-    {
-        // [Resize Rule 3] If we are are followed by a fixed column and we have a Stretch column before, we need to ensure
-        // that our left border won't move, which we can do by making sure column_a/column_b resizes cancels each others.
-        if (column_1 && (column_1->Flags & ImGuiTableColumnFlags_WidthFixed))
-            if (table->LeftMostStretchedColumn != -1 && table->Columns[table->LeftMostStretchedColumn].DisplayOrder < column_0->DisplayOrder)
-            {
-                // (old_a + old_b == new_a + new_b) --> (new_a == old_a + old_b - new_b)
-                float column_1_width = ImMax(column_1->WidthRequest - (column_0_width - column_0->WidthRequest), min_width);
-                column_0_width = column_0->WidthRequest + column_1->WidthRequest - column_1_width;
-                column_1->WidthRequest = column_1_width;
-            }
+    // [Resize Rule 1] Can't resize from right of right-most visible column if there is any Stretch column. Implemented in TableUpdateLayout().
 
-        // Apply
-        //IMGUI_DEBUG_LOG("TableSetColumnWidth(%d, %.1f->%.1f)\n", column_0_idx, column_0->WidthRequested, column_0_width);
-        column_0->WidthRequest = column_0_width;
-    }
-    else if (column_0->Flags & ImGuiTableColumnFlags_WidthStretch)
-    {
-        // We can also use previous column if there's no next one (this is used when doing an auto-fit on the right-most stretch column)
-        if (column_1 == NULL)
-            column_1 = (column_0->PrevEnabledColumn != -1) ? &table->Columns[column_0->PrevEnabledColumn] : NULL;
-        if (column_1 == NULL)
-            return;
-
-        if (column_1->Flags & ImGuiTableColumnFlags_WidthFixed)
-        {
-            // [Resize Rule 2]
-            float off = (column_0->WidthGiven - column_0_width);
-            float column_1_width = column_1->WidthGiven + off;
-            column_1->WidthRequest = ImMax(min_width, column_1_width);
-        }
-        else
+    // If we have all Fixed columns OR resizing a Fixed column that doesn't come after a Stretch one, we can do an offsetting resize.
+    // This is the preferred resize path
+    if (column_0->Flags & ImGuiTableColumnFlags_WidthFixed)
+        if (!column_1 || table->LeftMostStretchedColumn == -1 || table->Columns[table->LeftMostStretchedColumn].DisplayOrder >= column_0->DisplayOrder)
         {
-            // At this point column_1 is the next OR previous column and we know it is a stretch column.
-            // (old_a + old_b == new_a + new_b) --> (new_a == old_a + old_b - new_b)
-            float column_1_width = ImMax(column_1->WidthRequest - (column_0_width - column_0->WidthRequest), min_width);
-            column_0_width = column_0->WidthRequest + column_1->WidthRequest - column_1_width;
-            column_1->WidthRequest = column_1_width;
             column_0->WidthRequest = column_0_width;
-            TableUpdateColumnsWeightFromWidth(table);
+            table->IsSettingsDirty = true;
+            return;
         }
-    }
+
+    // We can also use previous column if there's no next one (this is used when doing an auto-fit on the right-most stretch column)
+    if (column_1 == NULL)
+        column_1 = (column_0->PrevEnabledColumn != -1) ? &table->Columns[column_0->PrevEnabledColumn] : NULL;
+    if (column_1 == NULL)
+        return;
+
+    // Resizing from right-side of a Stretch column before a Fixed column forward sizing to left-side of fixed column.
+    // (old_a + old_b == new_a + new_b) --> (new_a == old_a + old_b - new_b)
+    float column_1_width = ImMax(column_1->WidthRequest - (column_0_width - column_0->WidthRequest), min_width);
+    column_0_width = column_0->WidthRequest + column_1->WidthRequest - column_1_width;
+    column_0->WidthRequest = column_0_width;
+    column_1->WidthRequest = column_1_width;
+    if ((column_0->Flags | column_1->Flags) & ImGuiTableColumnFlags_WidthStretch)
+        TableUpdateColumnsWeightFromWidth(table);
+    table->IsSettingsDirty = true;
 }
 
 // Disable clipping then auto-fit, will take 2 frames
@@ -2715,7 +2694,7 @@ void ImGui::TableHeader(const char* label)
     bool pressed = ButtonBehavior(bb, id, &hovered, &held, ImGuiButtonFlags_AllowItemOverlap);
     if (g.ActiveId != id)
         SetItemAllowOverlap();
-    if (hovered || selected)
+    if (held || hovered || selected)
     {
         const ImU32 col = GetColorU32(held ? ImGuiCol_HeaderActive : hovered ? ImGuiCol_HeaderHovered : ImGuiCol_Header);
         //RenderFrame(bb.Min, bb.Max, col, false, 0.0f);