Revert "Correct GC offset calculation #788"

- This reverts commit 657fffb.
- This created a regression on Mac
- See #1067

Author: Phillipus

bundles/org.eclipse.swt/Eclipse SWT/cocoa/org/eclipse/swt/graphics/GC.java

@@ -469,28 +469,23 @@ NSAutoreleasePool checkGC (int mask) {
 		path.setLineCapStyle(capStyle);
 	}
 	if ((state & DRAW_OFFSET) != 0) {
-		boolean isAntiAliasingActive = getAntialias() != SWT.OFF;
-		int effectiveLineWidth = data.lineWidth < 1 ? 1 : Math.round(data.lineWidth);
-		if (isAntiAliasingActive || effectiveLineWidth % 2 == 1) {
-			NSSize offset = new NSSize();
-			// In case the effective line width is odd or anti-aliasing is used, add (0.5, 0.5) to coordinates in
-			// the coordinate system in which drawings are performed.
-			// I.e., a line starting at (0,0) will effectively start in pixel right below
-			// that coordinate with its center at (0.5, 0.5).
-			offset.width = offset.height = 0.5f;
-			if (!isAntiAliasingActive) {
-				offset.width /= effectiveLineWidth;
-				offset.height /= effectiveLineWidth;
-			}
-			// The offset will be applied to the coordinate system of the GC; so transform
-			// it from the drawing coordinate system to the coordinate system of the GC by
-			// applying the inverse transformation as the one applied to the GC and correct
-			// it by the line width.
-			if (data.inverseTransform != null) {
-				data.inverseTransform.transformSize(offset);
-			}
-			data.drawXOffset = Math.abs(offset.width);
-			data.drawYOffset = Math.abs(offset.height);
+		data.drawXOffset = data.drawYOffset = 0;
+		NSSize size = new NSSize();
+		size.width = size.height = 1;
+		if (data.transform != null) {
+			size = data.transform.transformSize(size);
+		}
+		double scaling = size.width;
+		if (scaling < 0) scaling = -scaling;
+		double strokeWidth = data.lineWidth * scaling;
+		if (strokeWidth == 0 || ((int)strokeWidth % 2) == 1) {
+			data.drawXOffset = 0.5f / scaling;
+		}
+		scaling = size.height;
+		if (scaling < 0) scaling = -scaling;
+		strokeWidth = data.lineWidth * scaling;
+		if (strokeWidth == 0 || ((int)strokeWidth % 2) == 1) {
+			data.drawYOffset = 0.5f / scaling;
 		}
 	}
 	return pool;

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/graphics/GC.java

@@ -379,33 +379,23 @@ void checkGC (int mask) {
 		Cairo.cairo_set_miter_limit(cairo, data.lineMiterLimit);
 	}
 	if ((state & DRAW_OFFSET) != 0) {
-		boolean isAntiAliasingActive = getAntialias() != SWT.OFF;
-		int effectiveLineWidth = data.lineWidth < 1 ? 1 : Math.round(data.lineWidth);
-		if (isAntiAliasingActive || effectiveLineWidth % 2 == 1) {
-			double[] offsetX = new double[]{1};
-			double[] offsetY = new double[]{1};
-			// In case the effective line width is odd or anti-aliasing is used, add (0.5, 0.5) to coordinates in
-			// the coordinate system in which drawings are performed.
-			// I.e., a line starting at (0,0) will effectively start in pixel right below
-			// that coordinate with its center at (0.5, 0.5).
-			offsetX[0] = offsetY[0] = 0.5f;
-			if (!isAntiAliasingActive) {
-				offsetX[0] /= effectiveLineWidth;
-				offsetY[0] /= effectiveLineWidth;
-			}
-			// The offset will be applied to the coordinate system of the GC; so transform
-			// it from the drawing coordinate system to the coordinate system of the GC by
-			// applying the inverse transformation as the one applied to the GC and correct
-			// it by the line width.
-			double[] matrix = new double[6];
-			Cairo.cairo_get_matrix(cairo, matrix);
-			double[] inverseMatrix = Arrays.copyOf(matrix, 6);
-			Cairo.cairo_matrix_invert(inverseMatrix);
-			Cairo.cairo_set_matrix(cairo, inverseMatrix);
-			Cairo.cairo_user_to_device_distance(cairo, offsetX, offsetY);
-			Cairo.cairo_set_matrix(cairo, matrix);
-			data.cairoXoffset = Math.abs(offsetX[0]);
-			data.cairoYoffset = Math.abs(offsetY[0]);
+		data.cairoXoffset = data.cairoYoffset = 0;
+		double[] matrix = new double[6];
+		Cairo.cairo_get_matrix(cairo, matrix);
+		double[] dx = new double[]{1};
+		double[] dy = new double[]{1};
+		Cairo.cairo_user_to_device_distance(cairo, dx, dy);
+		double scaling = dx[0];
+		if (scaling < 0) scaling = -scaling;
+		double strokeWidth = data.lineWidth * scaling;
+		if (strokeWidth == 0 || ((int)strokeWidth % 2) == 1) {
+			data.cairoXoffset = 0.5 / scaling;
+		}
+		scaling = dy[0];
+		if (scaling < 0) scaling = -scaling;
+		strokeWidth = data.lineWidth * scaling;
+		if (strokeWidth == 0 || ((int)strokeWidth % 2) == 1) {
+			data.cairoYoffset = 0.5 / scaling;
 		}
 	}
 }

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/GC.java

@@ -323,30 +323,24 @@ void checkGC(int mask) {
 			data.gdipFont = gdipFont;
 		}
 		if ((state & DRAW_OFFSET) != 0) {
-			boolean isAntiAliasingActive = getAntialias() != SWT.OFF;
-			int effectiveLineWidth = data.lineWidth < 1 ? 1 : Math.round(data.lineWidth);
-			if (isAntiAliasingActive || effectiveLineWidth % 2 == 1) {
-				PointF offset = new PointF();
-				// In case the effective line width is odd or anti-aliasing is used, add (0.5, 0.5) to coordinates in
-				// the coordinate system in which drawings are performed.
-				// I.e., a line starting at (0,0) will effectively start in pixel right below
-				// that coordinate with its center at (0.5, 0.5).
-				offset.X = offset.Y = 0.5f;
-				if (!isAntiAliasingActive) {
-					offset.X /= effectiveLineWidth;
-					offset.Y /= effectiveLineWidth;
-				}
-				// The offset will be applied to the coordinate system of the GC; so transform
-				// it from the drawing coordinate system to the coordinate system of the GC by
-				// applying the inverse transformation as the one applied to the GC and correct
-				// it by the line width.
-				long newMatrix = Gdip.Matrix_new(1, 0, 0, 1, 0, 0);
-				Gdip.Graphics_GetTransform(gdipGraphics, newMatrix);
-				Gdip.Matrix_Invert(newMatrix);
-				Gdip.Matrix_TransformVectors(newMatrix, offset, 1);
-				Gdip.Matrix_delete(newMatrix);
-				data.gdipXOffset = Math.abs(offset.X);
-				data.gdipYOffset = Math.abs(offset.Y);
+			data.gdipXOffset = data.gdipYOffset = 0;
+			long matrix = Gdip.Matrix_new(1, 0, 0, 1, 0, 0);
+			PointF point = new PointF();
+			point.X = point.Y = 1;
+			Gdip.Graphics_GetTransform(gdipGraphics, matrix);
+			Gdip.Matrix_TransformVectors(matrix, point, 1);
+			Gdip.Matrix_delete(matrix);
+			float scaling = point.X;
+			if (scaling < 0) scaling = -scaling;
+			float penWidth = data.lineWidth * scaling;
+			if (penWidth == 0 || (((int)penWidth) & 1) == 1) {
+				data.gdipXOffset = 0.5f / scaling;
+			}
+			scaling = point.Y;
+			if (scaling < 0) scaling = -scaling;
+			penWidth = data.lineWidth * scaling;
+			if (penWidth == 0 || (((int)penWidth) & 1) == 1) {
+				data.gdipYOffset = 0.5f / scaling;
 			}
 		}
 		return;

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_graphics_GC.java

@@ -15,9 +15,6 @@
 package org.eclipse.swt.tests.junit;
 
 import static org.eclipse.swt.tests.junit.SwtTestUtil.assertSWTProblem;
-import static org.hamcrest.MatcherAssert.assertThat;
-import static org.hamcrest.Matchers.is;
-import static org.hamcrest.Matchers.not;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -38,7 +35,6 @@
 import org.eclipse.swt.graphics.Point;
 import org.eclipse.swt.graphics.RGB;
 import org.eclipse.swt.graphics.Rectangle;
-import org.eclipse.swt.graphics.Transform;
 import org.eclipse.swt.internal.DPIUtil;
 import org.eclipse.swt.widgets.Canvas;
 import org.eclipse.swt.widgets.Display;
@@ -737,35 +733,6 @@ public void test_bug493455_drawImageAlpha_srcPos() {
 
 }
 
-/**
- * @see <a href="https://github.com/eclipse-platform/eclipse.platform.swt/issues/788">Issue 788</a>
- */
-@Test
-public void test_drawLine_noSingularitiesIn45DregreeRotation() {
-	int imageSize = 3;
-	int centerPixel = imageSize / 2;
-	Image image = new Image(Display.getDefault(), imageSize, imageSize);
-	GC gc = new GC(image);
-	Transform rotation = new Transform(gc.getDevice());
-	gc.getTransform(rotation);
-
-	try {
-		// Rotate 45° around image center
-		rotation.translate(centerPixel, centerPixel);
-		rotation.rotate(45);
-		rotation.translate(- centerPixel, - centerPixel);
-		gc.setTransform(rotation);
-		gc.drawLine(centerPixel, centerPixel, centerPixel + 1, centerPixel);
-
-		assertThat("line is not drawn with 45 degree rotation",
-				image.getImageData().getPixel(centerPixel, centerPixel), not(is(-1)));
-	} finally {
-		rotation.dispose();
-		gc.dispose();
-		image.dispose();
-	}
-}
-
 /* custom */
 Display display;
 Shell shell;