fix up a few long-standing display quirks:

- don't clear the display when toggling fullscreen
- clear the overscan area when disabling overscan (for PAL window sizes)
- always actively draw to the display even when no cart is loaded,
rather than relying on the blank canvas widget to always get drawn
correctly
- properly clear some video drivers' buffer (e.g. OpenGL) on startup

bsnes/ruby/video/opengl.hpp

@@ -43,6 +43,7 @@ public:
     iheight = max(height, iheight);
     if(buffer) delete[] buffer;
     buffer = new uint32_t[iwidth * iheight];
+    clear();
 
     glBindTexture(GL_TEXTURE_2D, gltexture);
     glPixelStorei(GL_UNPACK_ROW_LENGTH, iwidth);

bsnes/ruby/video/sdl.cpp

@@ -50,6 +50,7 @@ public:
       SDL_SWSURFACE, iwidth, iheight, 32,
       0x00ff0000, 0x0000ff00, 0x000000ff, 0xff000000
     );
+    clear();
   }
 
   bool lock(uint32_t *&data, unsigned &pitch, unsigned width, unsigned height) {

bsnes/snes/alt/ppu/ppu.cpp

@@ -102,10 +102,12 @@ void PPU::scanline() {
 }
 
 void PPU::render_scanline() {
+  if(framecounter) return;
   if(line >= 1 && line < (!overscan() ? 225 : 240)) {
-    if(framecounter) return;
     render_line_oam_rto();
     render_line();
+  } else if(line >= 1 && line < 240) {
+    render_line_clear();
   }
 }
 

bsnes/snes/ppu/ppu.cpp

@@ -144,6 +144,8 @@ void PPU::frame() {
   oam.frame();
 
   display.interlace = regs.interlace;
+  if (display.overscan && !regs.overscan)
+    memset(output + 225 * 1024, 0, 15 * 1024 * sizeof(uint16));
   display.overscan = regs.overscan;
 }
 

bsnes/ui-qt/base/main.cpp

@@ -724,9 +724,7 @@ void CanvasObject::mouseMoveEvent(QMouseEvent *event) {
 //custom video render and mouse capture functionality
 
 QPaintEngine* CanvasWidget::paintEngine() const {
-  if(SNES::cartridge.loaded()) {
-    video.refresh();
-  }
+  video.refresh();
   return 0;
 }
 

bsnes/ui-qt/utility/system-state.cpp

@@ -104,7 +104,7 @@ void Utility::modifySystemState(system_state_t systemState) {
 
   if(!application.power) unacquireMouse();
 
-  // don't let widget updates temporarily draw a parent widget over an external rendering contex
+  // don't let widget updates temporarily draw a parent widget over an external rendering context
   // (only applies when the system is powered on)
   mainWindow->canvas->setUpdatesEnabled(!application.power || video.cap("QWidget"));
 

bsnes/ui-qt/utility/window.cpp

@@ -1,6 +1,4 @@
 void Utility::updateFullscreenState() {
-  video.clear();
-
   if(config().video.isFullscreen == false) {
     config().video.context = &config().video.windowed;
     mainWindow->showNormal();