Fix bugtracker #112: no snap in the symbol editor below 100 % zoom

Below 100 % ElementView::drawBackground() hid the grid and also set the
snap step to 1 unit, so anything dragged while zoomed out landed off the
grid with nothing on screen to show it. A large symbol opens fitted to
the window below 100 %, which is why the report also says "when the
selection is big".

Keep hiding the grid below 100 % (its dots would merge into a grey
wash), but snap every 10 units, as at 100 %. The zoom-to-grid rule moves
into a header-only ElementViewGrid so it can be tested without an
editor window, like textgrid.h.

Checked in the editor: a one-rectangle symbol zoomed out to about 0.6x,
its edge dragged by (15, 10) px and saved: master moves it by (28, 18),
this branch by (30, 20). tst_elementviewgrid fails with the old step 1
and passes now; ctest 45/45.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

sources/editor/elementview.cpp

@@ -17,6 +17,8 @@
 */
 #include "elementview.h"
 
+#include "elementviewgrid.h"
+
 #include "../qetapp.h"
 #include "UndoCommand/pastepartscommand.h"
 #include "ui/qetelementeditor.h"
@@ -535,27 +537,11 @@ void ElementView::drawBackground(QPainter *p, const QRectF &r) {
 
 	// choisit la granularite de la grille en fonction du zoom en cours
 	// selects the grid granularity according to the current zoom level
-	int drawn_x_grid = 1;//scene_ -> xGrid();
-	int drawn_y_grid = 1;//scene_ -> yGrid();
-	bool draw_grid = true;
-	bool draw_cross = false;
-
-	if (zoom_factor < 1.0) { //< no grid
-		draw_grid = false;
-	} else if (zoom_factor < 4.0) { //< grid 10*10
-		drawn_x_grid *= 10;
-		drawn_y_grid *= 10;
-	}else if (zoom_factor < 8.0) { //< grid 5*5
-		drawn_x_grid *= 5;
-		drawn_y_grid *= 5;
-		draw_cross = true;
-	} else if (zoom_factor < 10.0) { //< grid 2*2
-		drawn_x_grid *= 2;
-		drawn_y_grid *= 2;
-		draw_cross = true;
-	} else { //< grid 1*1
-		draw_cross = true;
-	}
+	const ElementViewGrid grid = ElementViewGrid::forZoom(zoom_factor);
+	const int drawn_x_grid = grid.step;
+	const int drawn_y_grid = grid.step;
+	const bool draw_grid = grid.draw_grid;
+	const bool draw_cross = grid.draw_cross;
 
 	m_scene->setGrid(drawn_x_grid, drawn_y_grid);
 

sources/editor/elementviewgrid.h

@@ -0,0 +1,60 @@
+/*
+	Copyright 2006-2026 The QElectroTech Team
+	This file is part of QElectroTech.
+
+	QElectroTech is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 2 of the License, or
+	(at your option) any later version.
+
+	QElectroTech is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with QElectroTech.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#ifndef ELEMENTVIEWGRID_H
+#define ELEMENTVIEWGRID_H
+
+#include <QtGlobal>
+
+/**
+	The symbol editor's grid at a given zoom: the step parts snap to, and
+	how the grid is drawn. The step gets finer as the view zooms in, so a
+	small detail can be placed precisely.
+
+	Below 100 % the grid is not drawn (its dots would merge into a grey
+	wash), but parts still snap every 10 units, as at 100 %. Snapping to 1
+	unit there left everything dragged while zoomed out off the grid, with
+	nothing on screen to show it (bugtracker #112).
+*/
+struct ElementViewGrid
+{
+	int step = 10;
+	bool draw_grid = true;
+	bool draw_cross = false;
+
+	static ElementViewGrid forZoom(qreal zoom_factor)
+	{
+		ElementViewGrid grid;
+		if (zoom_factor < 1.0) {
+			grid.draw_grid = false;
+		} else if (zoom_factor < 4.0) {
+			grid.step = 10;
+		} else if (zoom_factor < 8.0) {
+			grid.step = 5;
+			grid.draw_cross = true;
+		} else if (zoom_factor < 10.0) {
+			grid.step = 2;
+			grid.draw_cross = true;
+		} else {
+			grid.step = 1;
+			grid.draw_cross = true;
+		}
+		return grid;
+	}
+};
+
+#endif // ELEMENTVIEWGRID_H

tests/qttest/CMakeLists.txt

@@ -104,6 +104,13 @@ add_test(NAME tst_textgrid COMMAND tst_textgrid)
 target_include_directories(tst_textgrid PRIVATE ${QET_DIR}/sources)
 target_link_libraries(tst_textgrid PRIVATE Qt::Test)
 
+# elementviewgrid.h is header-only: the symbol editor's snap step at each
+# zoom (bugtracker #112), tested without an editor window.
+add_executable(tst_elementviewgrid tst_elementviewgrid.cpp)
+add_test(NAME tst_elementviewgrid COMMAND tst_elementviewgrid)
+target_include_directories(tst_elementviewgrid PRIVATE ${QET_DIR}/sources)
+target_link_libraries(tst_elementviewgrid PRIVATE Qt::Test)
+
 # alignment.h is header-only too (it builds on textgrid.h): the geometry
 # behind the align commands, tested without a scene.
 add_executable(tst_alignment tst_alignment.cpp)

tests/qttest/tst_elementviewgrid.cpp

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <QtTest>
+
+#include "editor/elementviewgrid.h"
+
+// The symbol editor's snap step at each zoom (bugtracker #112): below
+// 100 % the grid is hidden but parts must still snap every 10 units.
+class tst_elementviewgrid : public QObject
+{
+	Q_OBJECT
+
+private slots:
+	void stepAtZoom_data()
+	{
+		QTest::addColumn<qreal>("zoom");
+		QTest::addColumn<int>("step");
+		QTest::addColumn<bool>("drawGrid");
+		QTest::addColumn<bool>("drawCross");
+
+		QTest::newRow("10 % (fit to a big symbol)") << 0.10 << 10 << false << false;
+		QTest::newRow("62.5 %, the #112 case")      << 0.625 << 10 << false << false;
+		QTest::newRow("100 %")                      << 1.0  << 10 << true  << false;
+		QTest::newRow("200 %")                      << 2.0  << 10 << true  << false;
+		QTest::newRow("400 %")                      << 4.0  << 5  << true  << true;
+		QTest::newRow("800 %")                      << 8.0  << 2  << true  << true;
+		QTest::newRow("1000 %")                     << 10.0 << 1  << true  << true;
+	}
+
+	void stepAtZoom()
+	{
+		QFETCH(qreal, zoom);
+		QFETCH(int, step);
+		QFETCH(bool, drawGrid);
+		QFETCH(bool, drawCross);
+
+		const ElementViewGrid grid = ElementViewGrid::forZoom(zoom);
+		QCOMPARE(grid.step, step);
+		QCOMPARE(grid.draw_grid, drawGrid);
+		QCOMPARE(grid.draw_cross, drawCross);
+	}
+};
+
+QTEST_APPLESS_MAIN(tst_elementviewgrid)
+
+#include "tst_elementviewgrid.moc"