314 lines
11 KiB
ArmAsm
314 lines
11 KiB
ArmAsm
; Renders a frame of animation
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;
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; The render function is the point of committment -- most of the APIs that set sprites and
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; update coordinates are lazy; they simply save their values and set a dirty flag in the
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; DirtyBits word.
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;
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; This function examines the dirty bits and actually performs the work to update the code field
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; and internal data structure to properly render the play field. Then the update pipeline is
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; executed.
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;
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; Everything is composited into the tiles in the playfield and then the screen is rendered in
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; a single pass.
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;
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; TODO -- actually check the dirty bits and be selective on what gets updated. For example, if
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; only the Y position changes, then we should only need to set new values on the
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; virtual lines that were brought on screen. If the X position only changes by one
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; byte, then we may have to change the CODE_ENTRY values or restore/set new OPCODE
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; values, but not both.
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; It's important to do _ApplyBG0YPos first because it calculates the value of StartY % 208 which is
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; used in all of the other loops
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_Render
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sta RenderFlags
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lda LastRender ; Check to see what kind of rendering was done on the last frame. If
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beq :no_change ; it was not this renderer,
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jsr _ResetToNormalTileProcs
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jsr _Refresh
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:no_change
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jsr _DoTimers ; Run any pending timer tasks
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stz SpriteRemovedFlag ; If we remove a sprite, then we need to flag a rebuild for the next frame
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; If we are doing per-scanline rendering, use the alternate renderer
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lda #RENDER_PER_SCANLINE
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bit RenderFlags
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beq *+5
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jmp _RenderScanlines ; Do the scanline-based renderer
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jsr _ApplyBG0YPos ; Set stack addresses for the virtual lines to the physical screen
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lda #RENDER_BG1_ROTATION
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bit RenderFlags
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bne :skip_bg1_y
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jsr _ApplyBG1YPos ; Set the y-register values of the blitter
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:skip_bg1_y
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; _ApplyBG0Xpos need to be split because we have to set the offsets, then draw in any updated tiles, and
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; finally patch out the code field. Right now, the BRA operand is getting overwritten by tile data.
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jsr _ApplyBG0XPosPre
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jsr _ApplyBG1XPosPre
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jsr _RenderSprites ; Once the BG0 X and Y positions are committed, update sprite data
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jsr _UpdateBG0TileMap ; and the tile maps. These subroutines build up a list of tiles
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; jsr _UpdateBG1TileMap ; that need to be updated in the code field
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jsr _ApplyTiles ; This function actually draws the new tiles into the code field
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jsr _ApplyBG0XPos ; Patch the code field instructions with exit BRA opcode
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lda #RENDER_BG1_ROTATION
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bit RenderFlags
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bne :skip_bg1_x
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jsr _ApplyBG1XPos ; Update the direct page value based on the horizontal position
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:skip_bg1_x
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; The code fields are locked in now and ready to be rendered. See if there is an overlay or any
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; other reason to render with shadowing off. Otherwise, just do things quickly.
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lda Overlays
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beq :no_ovrly
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jsr _ShadowOff
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; Shadowing is turned off. Render all of the scan lines that need a second pass. One
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; optimization that can be done here is that the lines can be rendered in any order
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; since it is not shown on-screen yet.
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ldx Overlays+2 ; Blit the full virtual buffer to the screen
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ldy Overlays+4
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jsr _BltRange
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; Turn shadowing back on
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jsr _ShadowOn
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; Now render all of the remaining lines in top-to-bottom (or bottom-to-top) order
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ldx #0
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ldy Overlays+2
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beq :skip
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jsr _BltRange
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:skip
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jsr _DoOverlay
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ldx Overlays+4
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cpx ScreenHeight
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beq :done
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ldy ScreenHeight
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jsr _BltRange
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bra :done
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:no_ovrly
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ldx #0 ; Blit the full virtual buffer to the screen
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ldy ScreenHeight
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jsr _BltRange
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:done
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ldx #0
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ldy ScreenHeight
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jsr _BltSCB
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lda StartYMod208 ; Restore the fields back to their original state
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ldx ScreenHeight
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jsr _RestoreBG0Opcodes
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lda StartY
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sta OldStartY
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lda StartX
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sta OldStartX
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lda BG1StartY
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sta OldBG1StartY
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lda BG1StartX
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sta OldBG1StartX
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stz DirtyBits
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stz LastRender ; Mark that a full render was just performed
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lda SpriteRemovedFlag ; If any sprite was removed, set the rebuild flag
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beq :no_removal
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lda #DIRTY_BIT_SPRITE_ARRAY
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sta DirtyBits
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:no_removal
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rts
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_DoOverlay
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lda Overlays+6
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stal :disp+1
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lda Overlays+7
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stal :disp+2
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lda ScreenY0 ; pass the address of the first line of the overlay
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clc
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adc Overlays+2
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asl
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tax
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lda ScreenAddr,x
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clc
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adc ScreenX0
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:disp jsl $000000
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rts
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; Use the per-scanline tables to set the screen. This is really meant to be used without the built-in tilemap
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; support and is more of a low-level way to control the background rendering
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_RenderScanlines
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jsr _ApplyBG0YPos ; Set stack addresses for the virtual lines to the physical screen
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; jsr _ApplyBG1YPos ; Set the y-register values of the blitter
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; _ApplyBG0Xpos need to be split because we have to set the offsets, then draw in any updated tiles, and
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; finally patch out the code field. Right now, the BRA operand is getting overwritten by tile data.
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jsr _ApplyBG0XPosPre
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; jsr _ApplyBG1XPosPre
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; jsr _RenderSprites ; Once the BG0 X and Y positions are committed, update sprite data
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; jsr _ApplyTiles ; This function actually draws the new tiles into the code field
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jsr _ScanlineBG0XPos ; Patch the code field instructions with exit BRA opcode
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; jsr _ApplyBG1XPos ; Update the direct page value based on the horizontal position
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; The code fields are locked in now and ready to be rendered. See if there is an overlay or any
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; other reason to render with shadowing off. Otherwise, just do things quickly.
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lda Overlays
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beq :no_ovrly
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jsr _ShadowOff
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; Shadowing is turned off. Render all of the scan lines that need a second pass. One
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; optimization that can be done here is that the lines can be rendered in any order
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; since it is not shown on-screen yet.
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ldx Overlays+2 ; Blit the full virtual buffer to the screen
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ldy Overlays+4
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jsr _BltRange
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; Turn shadowing back on
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jsr _ShadowOn
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; Now render all of the remaining lines in top-to-bottom (or bottom-to-top) order
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ldx #0
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ldy Overlays+2
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beq :skip
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jsr _BltRange
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:skip
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jsr _DoOverlay
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ldx Overlays+4
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cpx ScreenHeight
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beq :done
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ldy ScreenHeight
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jsr _BltRange
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bra :done
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:no_ovrly
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ldx #0 ; Blit the full virtual buffer to the screen
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ldy ScreenHeight
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jsr _BltRange
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:done
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ldx #0
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ldy ScreenHeight
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jsr _BltSCB
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lda StartYMod208 ; Restore the fields back to their original state
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ldx ScreenHeight
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jsr _RestoreScanlineBG0Opcodes
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lda StartY
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sta OldStartY
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lda StartX
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sta OldStartX
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lda BG1StartY
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sta OldBG1StartY
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lda BG1StartX
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sta OldBG1StartX
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stz DirtyBits
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stz LastRender ; Mark that a full render was just performed
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lda SpriteRemovedFlag ; If any sprite was removed, set the rebuild flag
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beq :no_removal
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lda #DIRTY_BIT_SPRITE_ARRAY
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sta DirtyBits
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:no_removal
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rts
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; Run through all of the tiles on the DirtyTile list and render them
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_ApplyTiles
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ldx DirtyTileCount
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phd ; sve the current direct page
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tdc
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clc
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adc #$100 ; move to the next page
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tcd
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stx DP2_DIRTY_TILE_COUNT ; Cache the dirty tile count
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jsr _PopDirtyTilesFast
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pld ; Move back to the original direct page
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stz DirtyTileCount ; Reset the dirty tile count
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rts
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; This is a specialized render function that only updates the dirty tiles *and* draws them
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; directly onto the SHR graphics buffer. The playfield is not used at all. In some way, this
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; ignores almost all of the capabilities of GTE, but it does provide a convenient way to use
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; the sprite subsystem + tile attributes for single-screen games which should be able to run
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; close to 60 fps.
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;
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; In this renderer, we assume that there is no scrolling, so no need to update any information about
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; the BG0/BG1 positions
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_RenderDirty
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lda LastRender ; If the full renderer was last called, we assume that
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bne :norecalc ; the scroll positions have likely changed, so recalculate
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jsr _RecalcTileScreenAddrs ; them to make sure sprites draw at the correct screen address
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jsr _ResetToDirtyTileProcs ; Switch the tile procs to the dirty tile rendering functions
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; jsr _ClearSpritesFromCodeField ; Restore the tiles to their non-sprite versions
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:norecalc
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jsr _RenderSprites
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jsr _ApplyDirtyTiles
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lda #1
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sta LastRender
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rts
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_ApplyDirtyTiles
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phd ; save the current direct page
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tdc
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clc
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adc #$100 ; move to the next page
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tcd
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bra :begin
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:loop
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; Retrieve the offset of the next dirty Tile Store items in the Y-register
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jsr _PopDirtyTile2
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; Call the generic dispatch with the Tile Store record pointer at by the Y-register.
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jsr _RenderDirtyTile
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; Loop again until the list of dirty tiles is empty
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:begin ldy DirtyTileCount
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bne :loop
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pld ; Move back to the original direct page
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stz DirtyTileCount ; Reset the dirty tile count
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rts
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