Hide the cursor only when capturing the mouse

Clean up mouse cursor code to use ImGuiMouseCursor_None
Ignore Pi::DrawGUI as it doesn't make sense for cursors

src/Input.cpp

@@ -290,6 +290,10 @@ float Input::JoystickAxisState(int joystick, int axis)
 
 void Input::SetCapturingMouse(bool grabbed)
 {
+	// early-out to avoid changing (possibly) expensive WM state
+	if (grabbed == m_capturingMouse)
+		return;
+
 	SDL_SetWindowGrab(Pi::renderer->GetSDLWindow(), SDL_bool(grabbed));
 	SDL_SetRelativeMouseMode(SDL_bool(grabbed));
 	m_capturingMouse = grabbed;

src/Input.h

@@ -132,7 +132,14 @@ public:
 		memcpy(motion, mouseMotion, sizeof(int) * 2);
 	}
 
+	// Capturing the mouse hides the cursor, puts the mouse into relative mode,
+	// and passes all mouse inputs to the input system, regardless of whether
+	// ImGui is using them or not.
 	bool IsCapturingMouse() const { return m_capturingMouse; }
+
+	// Set whether the application would like to capture the mouse.
+	// To avoid contention between different classes, please only call this when the state
+	// has actually changed.
 	void SetCapturingMouse(bool enabled);
 
 	sigc::signal<void, SDL_Keysym *> onKeyPress;

src/Pi.cpp

@@ -885,7 +885,8 @@ void Pi::HandleEvents()
 
 		Pi::pigui->ProcessEvent(&event);
 
-		if (Pi::pigui->WantCaptureMouse()) {
+		// Input system takes priority over mouse events when capturing the mouse
+		if (Pi::pigui->WantCaptureMouse() && !Pi::input.IsCapturingMouse()) {
 			// don't process mouse event any further, imgui already handled it
 			switch (event.type) {
 			case SDL_MOUSEBUTTONDOWN:

src/pigui/PiGui.cpp

@@ -4,6 +4,7 @@
 #include "PiGui.h"
 #include "Pi.h"
 #include "graphics/opengl/TextureGL.h" // nasty, usage of GL is implementation specific
+#include "imgui/imgui.h"
 // Use GLEW instead of GL3W.
 #define IMGUI_IMPL_OPENGL_LOADER_GLEW 1
 #include "imgui/examples/imgui_impl_opengl3.h"
@@ -375,15 +376,13 @@ void *PiGui::makeTexture(unsigned char *pixels, int width, int height)
 void PiGui::NewFrame(SDL_Window *window)
 {
 	PROFILE_SCOPED()
-	// Ask ImGui to hide OS cursor if GUI is not being drawn:
-	// it will do this if MouseDrawCursor is true. After the frame
-	// is created, we set the actual cursor draw state.
-#if 0 // Mouse cursors are set via the OS facilities.
-	// See also below.
-	if (!Pi::DrawGUI) {
-		ImGui::GetIO().MouseDrawCursor = true;
+
+	// Ask ImGui to hide OS cursor if we're capturing it for input:
+	// it will do this if GetMouseCursor == ImGuiMouseCursor_None.
+	if (Pi::input.IsCapturingMouse()) {
+		ImGui::SetMouseCursor(ImGuiMouseCursor_None);
 	}
-#endif
+
 	switch (Pi::renderer->GetRendererType()) {
 	default:
 	case Graphics::RENDERER_DUMMY:
@@ -398,14 +397,6 @@ void PiGui::NewFrame(SDL_Window *window)
 
 	Pi::renderer->CheckRenderErrors(__FUNCTION__, __LINE__);
 	ImGui::SetMouseCursor(ImGuiMouseCursor_Arrow);
-#if 0 // Mouse cursors are set via the OS facilities.
-	// We may want to revisit this at a later date.
-	if(Pi::DoingMouseGrab() || !Pi::DrawGUI) {
-		ImGui::GetIO().MouseDrawCursor = false;
-	} else {
-		ImGui::GetIO().MouseDrawCursor = true;
-	}
-#endif
 }
 
 void PiGui::RunHandler(double delta, std::string handler)