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Drawing the screen: FadeToColour

[NES version, Bank 3]

Name: FadeToColour [Show more] Type: Subroutine Category: Drawing the screen Summary: Reverse-fade the screen from black to full colour over the next four VBlanks Deep dive: Views and view types in NES Elite
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * FadeToColour_b3 calls FadeToColour
.FadeToColour JSR WaitForNMI ; Wait until the next NMI interrupt has passed (i.e. the ; next VBlank) JSR GetViewPalettes ; Get the palette for the view type in QQ11a and store ; it in a table at XX3 JSR FadeColoursTwice ; Fade the screen colours two steps towards black JSR FadeColours ; Fade the screen colours a third step towards black, so ; the palette in XX3 is now one step brighter than full ; black (as it takes four steps to fully black-out the ; normal palette) DEC updatePaletteInNMI ; Decrement updatePaletteInNMI to a non-zero value so we ; do send palette data from XX3 to the PPU during NMI, ; which will ensure the screen updates with the colours ; as we reverse the back to full colour JSR WaitFor2NMIs ; Wait until two NMI interrupts have passed (i.e. the ; next two VBlanks) JSR GetViewPalettes ; Get the palette for the view type in QQ11a and store ; it in a table at XX3 JSR FadeColoursTwice ; Fade the screen colours two steps towards black, so ; the palette in XX3 is now two steps brighter than full ; black JSR WaitFor2NMIs ; Wait until two NMI interrupts have passed (i.e. the ; next two VBlanks) JSR GetViewPalettes ; Get the palette for the view type in QQ11a and store ; it in a table at XX3 JSR FadeColours ; Fade the screen colours one step towards black, so the ; palette in XX3 is now three steps brighter than full ; black JSR WaitFor2NMIs ; Wait until two NMI interrupts have passed (i.e. the ; next two VBlanks) JSR GetViewPalettes ; Get the palette for the view type in QQ11a and store ; it in a table at XX3 JSR SetPaletteColours ; Set the view's palette from the entries in the XX3 ; palette table, so the screen is now at full brightness ; once again JSR WaitForNMI ; Wait until the next NMI interrupt has passed (i.e. the ; next VBlank) INC updatePaletteInNMI ; Increment updatePaletteInNMI back to the value it had ; before we decremented it above LSR screenFadedToBlack ; Clear bit 7 of screenFadedToBlack to indicate that the ; screen has faded back up to full colour RTS ; Return from the subroutine