Pass through draw_fb optimization metadata to Display class

The JS implementation does content hashing to not blit unchanged
framebuffer contents (see mihaip/dingusppc@171ff2d407).
However, that is not necessary for the ATI adapters that already track
this and only set draw_fb if the framebuffer has actually changed.

Pass through a fb_known_to_be_changed for these cases, and also add an
optional update_skipped method (since the JS still wants to know when
the last logical screen update was).

devices/video/atimach64gx.cpp

@@ -164,6 +164,8 @@ AtiMach64Gx::AtiMach64Gx()
     insert_bits<uint32_t>(this->regs[ATI_GUI_STAT], 32, ATI_FIFO_CNT, ATI_FIFO_CNT_size);
 
     set_bit(regs[ATI_CRTC_GEN_CNTL], ATI_CRTC_DISPLAY_DIS); // because blank_on is true
+
+    this->draw_fb_is_dynamic = true;
 }
 
 void AtiMach64Gx::change_one_bar(uint32_t &aperture, uint32_t aperture_size,

devices/video/atirage.cpp

@@ -144,6 +144,8 @@ ATIRage::ATIRage(uint16_t dev_id)
     this->regs[ATI_GP_IO] = ((mon_code & 6) << 11) | ((mon_code & 1) << 8);
     insert_bits<uint32_t>(this->regs[ATI_GUI_STAT], 32, ATI_FIFO_CNT, ATI_FIFO_CNT_size);
     set_bit(regs[ATI_CRTC_GEN_CNTL], ATI_CRTC_DISPLAY_DIS); // because blank_on is true
+
+    this->draw_fb_is_dynamic = true;
 }
 
 void ATIRage::change_one_bar(uint32_t &aperture, uint32_t aperture_size,

devices/video/display.h

@@ -41,9 +41,19 @@ public:
     // Clears the display
     void blank();
 
+
+    // Update the host framebuffer display. If the display adapter does its own
+    // dirty tracking, fb_known_to_be_changed will be set to true, so that the
+    // implementation can take that into account.
     void update(std::function<void(uint8_t *dst_buf, int dst_pitch)> convert_fb_cb,
                 std::function<void(uint8_t *dst_buf, int dst_pitch)> cursor_ovl_cb,
-                bool draw_hw_cursor, int cursor_x, int cursor_y);
+                bool draw_hw_cursor, int cursor_x, int cursor_y,
+                bool fb_known_to_be_changed);
+
+    // Called in cases where the framebuffer contents have not changed, so a
+    // normal update() call is not happening. Allows implementations that need
+    // to do per-frame bookkeeping to still do that.
+    void update_skipped();
 
     void handle_events(const WindowEvent& wnd_event);
     void setup_hw_cursor(std::function<void(uint8_t *dst_buf, int dst_pitch)> draw_hw_cursor,

devices/video/display_sdl.cpp

@@ -107,7 +107,8 @@ void Display::blank() {
 
 void Display::update(std::function<void(uint8_t *dst_buf, int dst_pitch)> convert_fb_cb,
                      std::function<void(uint8_t *dst_buf, int dst_pitch)> cursor_ovl_cb,
-                     bool draw_hw_cursor, int cursor_x, int cursor_y) {
+                     bool draw_hw_cursor, int cursor_x, int cursor_y,
+                     bool fb_known_to_be_changed) {
     if (impl->resizing)
         return;
 
@@ -137,6 +138,10 @@ void Display::update(std::function<void(uint8_t *dst_buf, int dst_pitch)> conver
     SDL_RenderPresent(impl->renderer);
 }
 
+void Display::update_skipped() {
+    // SDL implementation does not care about skipped updates.
+}
+
 void Display::setup_hw_cursor(std::function<void(uint8_t *dst_buf, int dst_pitch)> draw_hw_cursor,
                               int cursor_width, int cursor_height) {
     uint8_t*    dst_buf;

devices/video/videoctrl.cpp

@@ -81,7 +81,10 @@ void VideoCtrlBase::update_screen()
         }
         this->display.update(
             this->convert_fb_cb, this->cursor_ovl_cb,
-            this->cursor_on, cursor_x, cursor_y);
+            this->cursor_on, cursor_x, cursor_y,
+            this->draw_fb_is_dynamic);
+    } else if (this->draw_fb_is_dynamic) {
+        this->display.update_skipped();
     }
 }
 

devices/video/videoctrl.h

@@ -86,7 +86,12 @@ protected:
     int         pixel_format;
     float       pixel_clock;
     float       refresh_rate;
+
+    // Implementations may choose to track framebuffer writes and set draw_fb
+    // to false if updates can be skipped. If the do this, they should set
+    // draw_fb_is_dynamic at initialization time.
     bool        draw_fb = true;
+    bool        draw_fb_is_dynamic = false;
 
     uint32_t    palette[256] = {0}; // internal DAC palette in RGBA format