zoom around center of the screen

counter185 · May 16, 2024 · 6a35cab · 6a35cab
1 parent f469c83
commit 6a35cab
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Showing 2 changed files with 18 additions and 2 deletions.
diff --git a/freesprite/maineditor.cpp b/freesprite/maineditor.cpp
@@ -255,6 +255,22 @@ bool MainEditor::requestSafeClose() {
 	return false;
 }
 
+void MainEditor::zoom(int how_much)
+{
+	XY screenCenterPoint = XY{
+			(canvasCenterPoint.x - g_windowW/2) / -scale,
+			(canvasCenterPoint.y - g_windowH/2) / -scale
+	};
+	scale += how_much;
+	scale = scale < 1 ? 1 : scale;
+	XY onscreenPointNow = XY{
+		canvasCenterPoint.x + screenCenterPoint.x * scale,
+		canvasCenterPoint.y + screenCenterPoint.y * scale
+	};
+	XY pointDiff = xySubtract(XY{ g_windowW / 2, g_windowH / 2 }, onscreenPointNow);
+	canvasCenterPoint = xyAdd(canvasCenterPoint, pointDiff);
+}
+
 void MainEditor::takeInput(SDL_Event evt) {
 
 	if (evt.type == SDL_MOUSEBUTTONDOWN && evt.button.state) {
@@ -322,8 +338,7 @@ void MainEditor::takeInput(SDL_Event evt) {
 				}
 				break;
 			case SDL_MOUSEWHEEL:
-				scale += evt.wheel.y;
-				scale = scale < 1 ? 1 : scale;
+				zoom(evt.wheel.y);
 				break;
 			case SDL_KEYDOWN:
 				switch (evt.key.keysym.sym) {

diff --git a/freesprite/maineditor.h b/freesprite/maineditor.h
@@ -88,6 +88,7 @@ class MainEditor : public BaseScreen, public EventCallbackListener
 	void trySaveAsImage();
 	void recenterCanvas();
 	bool requestSafeClose();
+	void zoom(int how_much);
 
 	void checkAndDiscardEndOfUndoStack();
 	void commitStateToCurrentLayer();