MOHAWK: Rework Myst GFX updates

- Initial card state is drawn to the back buffer
- Script driven updates are drawn to the front buffer
Allows opcode 28 (copy back buffer to screen) and opcodes 29/33 (copy image to screen / back buffer) to work properly.
Fixes among others the generator room lights, and the matchbox.

svn-id: r54907

1 files changed, 3 insertions, 3 deletions

diff --git a/engines/mohawk/myst_stacks/selenitic.cpp b/engines/mohawk/myst_stacks/selenitic.cpp
index 183c92745d..161c90b6f5 100644
--- a/engines/mohawk/myst_stacks/selenitic.cpp
+++ b/engines/mohawk/myst_stacks/selenitic.cpp
@@ -872,12 +872,12 @@ void MystScriptParser_Selenitic::o_soundLockEndMove(uint16 op, uint16 var, uint1
 	*value = stepped;
 
 	slider->setStep(stepped);
-	slider->drawDataToScreen();
-	_vm->_gfx->updateScreen();
+	slider->restoreBackground();
+	slider->drawConditionalDataToScreen(1);
 
 	uint16 soundId = slider->getList3(0);
 	if (soundId)
-		_vm->_sound->playSoundBlocking(soundId);
+		_vm->_sound->playSound(soundId);
 
 	_vm->_sound->stopSound();
 	_vm->_sound->resumeBackground();