Add: [Emscripten] use "relative mouse mode" with SDL2

This mode doesn't wrap the mouse constantly, but requests SDL
to lock the mouse pointer. This is needed, as with Emscripten
you are not allowed to change the mouse poisition (only to lock
it into place).

1 files changed, 24 insertions, 0 deletions

diff --git a/src/gfx.cpp b/src/gfx.cpp
index 6039946fc..8027dad26 100644
--- a/src/gfx.cpp
+++ b/src/gfx.cpp
@@ -1785,6 +1785,30 @@ void SetAnimatedMouseCursor(const AnimCursor *table)
 }
 
 /**
+ * Update cursor position on mouse movement for relative modes.
+ * @param delta_x How much change in the X position.
+ * @param delta_y How much change in the Y position.
+ */
+void CursorVars::UpdateCursorPositionRelative(int delta_x, int delta_y)
+{
+	if (this->fix_at) {
+		this->delta.x = delta_x;
+		this->delta.y = delta_y;
+	} else {
+		int last_position_x = this->pos.x;
+		int last_position_y = this->pos.y;
+
+		this->pos.x = Clamp(this->pos.x + delta_x, 0, _cur_resolution.width - 1);
+		this->pos.y = Clamp(this->pos.y + delta_y, 0, _cur_resolution.height - 1);
+
+		this->delta.x = last_position_x - this->pos.x;
+		this->delta.y = last_position_y - this->pos.y;
+
+		this->dirty = true;
+	}
+}
+
+/**
  * Update cursor position on mouse movement.
  * @param x New X position.
  * @param y New Y position.