128 lines
4.6 KiB
ArmAsm
128 lines
4.6 KiB
ArmAsm
; Renders a frame of animation
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;
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; The rendering engine is built around the idea of compositing all of the moving components
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; on to the Bank 01 graphics buffer and then revealing everything in a single, vertical pass.
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;
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; If there was just a scrolling screen with no sprites, the screen would just get rendered
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; in a single pass, but it gets more complicated with sprites and various effects.
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;
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; Here is the high-level pipeline:
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;
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; 1. Identify row ranges with effects. These effects can be sprites or user-defined overlays
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; 2. Turn shadowing off
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; 3. Render the background for each effect row range (in any order)
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; 4. Render the sprites (in any order)
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; 5. Turn shadowing on
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; 6. Render the background for each non-effect row, a pei slam for sprite rows, and
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; the user-defined overlays (in sorted order)
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;
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; As a concrete example, consider:
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;
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; Rows 0 - 9 have a user-defined floating overlay for a score board
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; Rows 10 - 100 are background only
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; Rows 101 - 120 have one or more sprites
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; Rows 121 - 140 are background only
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; Rows 141 - 159 have a user-defined solid overlay for an animated platform
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;
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; A floating overlay means that some background data bay show through. A solid overlay means that
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; the user-defined data covers the entire scan line.
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;
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; The renderer would proceed as:
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;
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; - shadow off
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; - render_background(0, 10)
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; - render_background(101, 121)
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; - render_sprites()
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; - shadow_on
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; - render_user_overlay_1()
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; - render_background(10, 101)
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; - pei_slam(101, 121)
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; - render_background(121, 141)
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; - render_user_overlay_2()
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;
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; Generally speaking, a PEI Slam is faster that trying to do any sort of dirty-rectangle update by
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; tracking sprinte bounding boxes. But, if an application would benefit from skipping some background
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; drawing on sprite rows, that can be handled by using the low level routines to control the left/right
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; edges of the rendered play field.
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; The render function is the point of committment -- most of the APIs that set sprintes and
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; update coordinates are lazy; they simply save the value 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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Render ENT
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phb
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phk
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plb
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jsr _Render
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plb
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rtl
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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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jsr _ApplyBG0YPos ; Set stack addresses for the virtual lines to the physical screen
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jsr _ApplyBG1YPos
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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 _UpdateBG0TileMap
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jsr _UpdateBG1TileMap
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jsr _ApplyBG0XPos ; Patch the PEA instructions with exit BRA opcode
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jsr _ApplyBG1XPos ; Patch the PEA instructions with exit BRA opcode
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; The code fields are locked in now and reder to be rendered
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jsr _ShadowOff
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; ldx #0 ; Blit the full virtual buffer to the screen
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; ldy #8
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; jsr _BltRange
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jsr _ShadowOn
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; ldx #0 ; Expose the top 8 rows
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; ldy #8
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; jsr _PEISlam
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; ldx #0 ; Blit the full virtual buffer to the screen
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; ldy #16
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; jsr _BltRange
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; jsr Overlay
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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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lda StartY ; 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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rts
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