Make AR-changing resampling more user-friendly

Add modes where the borders to add or remove are automatically
calculated rather than forcing the user to do it manually, and hopefully
make it a bit clearer what exactly will happen.

src/dialog_resample.cpp

@@ -24,9 +24,10 @@
 #include "help_button.h"
 #include "libresrc/libresrc.h"
 #include "resolution_resampler.h"
+#include "validators.h"
 #include "video_context.h"
 
-#include <boost/rational.hpp>
+#include <boost/range/size.hpp>
 #include <wx/checkbox.h>
 #include <wx/sizer.h>
 #include <wx/spinctrl.h>
@@ -88,9 +89,9 @@ DialogResample::DialogResample(agi::Context *c, ResampleSettings &settings)
 	from_script = new wxButton(this, -1, _("From s&cript"));
 	from_script->Enable(false);
 
-	change_ar = new wxCheckBox(this, -1, _("&Change aspect ratio"));
-	change_ar->SetValidator(wxGenericValidator(&settings.change_ar));
-	change_ar->Enable(false);
+	wxString ar_modes[] = {_("Stretch"), _("Add borders"), _("Remove borders"), _("Manual")};
+	ar_mode = new wxRadioBox(this, -1, _("Aspect Ratio Handling"), wxDefaultPosition,
+		wxDefaultSize, boost::size(ar_modes), ar_modes, 1, 4, MakeEnumBinder(&settings.ar_mode));
 
 	// Position the controls
 	auto margin_sizer = new wxGridSizer(3, 3, 5, 5);
@@ -121,20 +122,24 @@ DialogResample::DialogResample(agi::Context *c, ResampleSettings &settings)
 
 	auto dest_res_box = new wxStaticBoxSizer(wxVERTICAL, this, _("Destination Resolution"));
 	dest_res_box->Add(dest_res_sizer, wxSizerFlags(1).Expand().Border(wxBOTTOM));
-	dest_res_box->Add(change_ar);
 
 	auto main_sizer = new wxBoxSizer(wxVERTICAL);
-	main_sizer->Add(margin_box, wxSizerFlags(1).Expand().Border());
 	main_sizer->Add(source_res_sizer, wxSizerFlags(0).Expand().Border());
 	main_sizer->Add(dest_res_box, wxSizerFlags(0).Expand().Border());
+	main_sizer->Add(ar_mode, wxSizerFlags(0).Expand().Border());
+	main_sizer->Add(margin_box, wxSizerFlags(1).Expand().Border());
 	main_sizer->Add(CreateStdDialogButtonSizer(wxOK | wxCANCEL | wxHELP), wxSizerFlags().Expand().Border(wxALL & ~wxTOP));
 	SetSizerAndFit(main_sizer);
 	CenterOnParent();
 
+	TransferDataToWindow();
+	UpdateButtons();
+
 	// Bind events
 	using std::bind;
 	Bind(wxEVT_BUTTON, bind(&HelpButton::OpenPage, "Resample resolution"), wxID_HELP);
 	Bind(wxEVT_SPINCTRL, [=](wxCommandEvent&) { UpdateButtons(); });
+	Bind(wxEVT_RADIOBOX, [=](wxCommandEvent&) { UpdateButtons(); });
 	from_video->Bind(wxEVT_BUTTON, &DialogResample::SetDestFromVideo, this);
 	from_script->Bind(wxEVT_BUTTON, &DialogResample::SetSourceFromScript, this);
 	symmetrical->Bind(wxEVT_CHECKBOX, &DialogResample::OnSymmetrical, this);
@@ -157,9 +162,18 @@ void DialogResample::UpdateButtons() {
 		(dest_x->GetValue() != video_w || dest_y->GetValue() != video_h));
 	from_script->Enable(source_x->GetValue() != script_w || source_y->GetValue() != script_h);
 
-	boost::rational<int> source_ar(source_x->GetValue(), source_y->GetValue());
-	boost::rational<int> dest_ar(dest_x->GetValue(), dest_y->GetValue());
-	change_ar->Enable(source_ar != dest_ar);
+	auto source_ar = double(source_x->GetValue()) / source_y->GetValue();
+	auto dest_ar = double(dest_x->GetValue()) / dest_y->GetValue();
+	bool ar_changed = abs(source_ar - dest_ar) / dest_ar > .01;
+
+	ar_mode->Enable(ar_changed);
+
+	bool margins = ar_changed && ar_mode->GetSelection() == (int)ResampleARMode::Manual;
+	symmetrical->Enable(margins);
+	margin_ctrl[LEFT]->Enable(margins);
+	margin_ctrl[TOP]->Enable(margins);
+	margin_ctrl[RIGHT]->Enable(margins && !symmetrical->GetValue());
+	margin_ctrl[BOTTOM]->Enable(margins && !symmetrical->GetValue());
 }
 
 void DialogResample::OnSymmetrical(wxCommandEvent &) {

src/dialog_resample.h

@@ -22,6 +22,7 @@
 namespace agi { struct Context; }
 class AssFile;
 class wxCheckBox;
+class wxRadioBox;
 class wxSpinCtrl;
 struct ResampleSettings;
 
@@ -42,7 +43,7 @@ class DialogResample final : public wxDialog {
 	wxSpinCtrl *dest_x;
 	wxSpinCtrl *dest_y;
 	wxCheckBox *symmetrical;
-	wxCheckBox *change_ar;
+	wxRadioBox *ar_mode;
 	wxSpinCtrl *margin_ctrl[4];
 
 	wxButton *from_script;

src/resolution_resampler.cpp

@@ -154,6 +154,36 @@ namespace {
 }
 
 void ResampleResolution(AssFile *ass, ResampleSettings settings) {
+	auto horizontal_stretch = 1.0;
+	auto old_ar = double(settings.source_x) / settings.source_y;
+	auto new_ar = double(settings.dest_x) / settings.dest_y;
+	bool border_horizontally = new_ar > old_ar;
+	// Don't convert aspect ratio if it's very close to correct
+	// (for reference, 848x480 <-> 1280x720 is .006)
+	if (abs(old_ar - new_ar) / new_ar > .01) {
+		switch (settings.ar_mode) {
+		case ResampleARMode::RemoveBorder:
+			border_horizontally = !border_horizontally;
+		case ResampleARMode::AddBorder:
+			if (border_horizontally) // Wider/Shorter
+				settings.margin[LEFT] = settings.margin[RIGHT] = (settings.source_y * new_ar - settings.source_x) / 2;
+			else // Taller/Narrower
+				settings.margin[TOP] = settings.margin[BOTTOM] = (settings.source_x / new_ar - settings.source_y) / 2;
+			break;
+		case ResampleARMode::Stretch:
+			horizontal_stretch = new_ar / old_ar;
+			break;
+		case ResampleARMode::Manual:
+			old_ar =
+				double(settings.source_x + settings.margin[LEFT] + settings.margin[RIGHT]) /
+				double(settings.source_y + settings.margin[TOP] + settings.margin[BOTTOM]);
+
+			if (abs(old_ar - new_ar) / new_ar > .01)
+				horizontal_stretch = new_ar / old_ar;
+			break;
+		}
+	}
+
 	// Add margins to original resolution
 	settings.source_x += settings.margin[LEFT] + settings.margin[RIGHT];
 	settings.source_y += settings.margin[TOP] + settings.margin[BOTTOM];
@@ -162,12 +192,9 @@ void ResampleResolution(AssFile *ass, ResampleSettings settings) {
 		settings.margin,
 		double(settings.dest_x) / double(settings.source_x),
 		double(settings.dest_y) / double(settings.source_y),
-		1.0
+		horizontal_stretch
 	};
 
-	if (settings.change_ar)
-		state.ar = state.rx / state.ry;
-
 	for (auto& line : ass->Styles)
 		resample_style(&state, line);
 	for (auto& line : ass->Events)

src/resolution_resampler.h

@@ -16,6 +16,13 @@
 
 class AssFile;
 
+enum class ResampleARMode {
+	Stretch,
+	AddBorder,
+	RemoveBorder,
+	Manual
+};
+
 /// Configuration parameters for a resample
 struct ResampleSettings {
 	int margin[4];  ///< Amount to add to each margin
@@ -23,7 +30,7 @@ struct ResampleSettings {
 	int source_y;   ///< Original Y resolution
 	int dest_x;     ///< New X resolution
 	int dest_y;     ///< New Y resolution
-	bool change_ar; ///< Should the aspect ratio of the subs be changed?
+	ResampleARMode ar_mode; ///< What to do if the old AR and new AR don't match
 };
 
 /// Resample the subtitles in the project

src/validators.h

@@ -76,6 +76,7 @@ class EnumBinder final : public wxValidator {
 	T *value;
 
 	wxObject *Clone() const override { return new EnumBinder<T>(value); }
+	bool Validate(wxWindow *) override { return true; }
 
 	bool TransferFromWindow() override {
 		if (wxRadioBox *rb = dynamic_cast<wxRadioBox*>(GetWindow()))