mirror of
https://github.com/lscharen/iigs-game-engine.git
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279 lines
8.3 KiB
ArmAsm
279 lines
8.3 KiB
ArmAsm
; An overlay is a callback from the render to shadow in a range of lines. At a minimum, the overlay
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; code needs to LDA/STA or TSB slam the data, but an overlay is typically used to draw some graphic
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; on top of the rendered playfield, such as a status bar or in-game message
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;
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; This overlay implementation is for a status bar that is 8-lines height that will be used to display some
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; status information. The interesting bit of this implementation is that it's split into two pieces,
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; a left and right section in order to be able to use the same code for different screen widths, but
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; still keep the content in the cornders while covering the full screen.
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;
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; There are two subroutines that need to be implemented -- one to update the overlay content and a
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; second to actually render to the screen
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; Initialize the overlay be drawin gin static content that will not change over time
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CHAR_TILE_BASE equ 241 ; set this to the real tile id that starts an ASCII run starting at '0' through 'Z'
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; Define the sizes of the left and right overlay buffers
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R_CHAR_COUNT equ 8 ; "TICK:XXX"
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L_CHAR_COUNT equ 7 ; "FPS:XXX"
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; Allocate a single buffer for holding both the left and right overlay characters + masks
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CHAR_WIDTH equ 4
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OVRLY_SPAN equ {{L_CHAR_COUNT+R_CHAR_COUNT}*CHAR_WIDTH}
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ovrly_buff ds OVRLY_SPAN*8
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ovrly_mask ds OVRLY_SPAN*8
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r_line equ ovrly_buff+{L_CHAR_COUNT*CHAR_WIDTH}
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l_line equ ovrly_buff
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r_mask equ ovrly_mask+{L_CHAR_COUNT*CHAR_WIDTH}
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l_mask equ ovrly_mask
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MASK_OFFSET equ {ovrly_mask-ovrly_buff}
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InitOverlay
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lda #'F'
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ldy #l_line+{CHAR_WIDTH*0}
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jsr _DrawChar
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lda #'P'
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ldy #l_line+{CHAR_WIDTH*1}
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jsr _DrawChar
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lda #'S'
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ldy #l_line+{CHAR_WIDTH*2}
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jsr _DrawChar
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lda #':'
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ldy #l_line+{CHAR_WIDTH*3}
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jsr _DrawChar
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lda #'T'
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ldy #r_line+{CHAR_WIDTH*0}
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jsr _DrawChar
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lda #'I'
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ldy #r_line+{CHAR_WIDTH*1}
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jsr _DrawChar
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lda #'C'
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ldy #r_line+{CHAR_WIDTH*2}
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jsr _DrawChar
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lda #'K'
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ldy #r_line+{CHAR_WIDTH*3}
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jsr _DrawChar
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lda #':'
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ldy #r_line+{CHAR_WIDTH*4}
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jsr _DrawChar
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rts
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; Update the dynamic content of the overlay
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_num2ascii
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and #$000F
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cmp #$000A
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bcc :out
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clc
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adc #'A'-'0'-10
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:out clc
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adc #'0'
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rts
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UdtOverlay
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lda frameCount ; render the FPS value
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xba
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jsr _num2ascii
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ldy #l_line+{CHAR_WIDTH*4}
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jsr _DrawChar
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lda frameCount
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lsr
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lsr
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lsr
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lsr
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jsr _num2ascii
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ldy #l_line+{CHAR_WIDTH*5}
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jsr _DrawChar
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lda frameCount
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jsr _num2ascii
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ldy #l_line+{CHAR_WIDTH*6}
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jsr _DrawChar
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ldal OneSecondCounter ; reder the number of remaining seconds
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xba
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jsr _num2ascii
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ldy #r_line+{CHAR_WIDTH*5}
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jsr _DrawChar
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ldal OneSecondCounter
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lsr
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lsr
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lsr
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lsr
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jsr _num2ascii
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ldy #r_line+{CHAR_WIDTH*6}
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jsr _DrawChar
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ldal OneSecondCounter
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jsr _num2ascii
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ldy #r_line+{CHAR_WIDTH*7}
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jsr _DrawChar
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rts
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; Draw the overlay
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; A = address of the left edge of the screen
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Overlay ENT
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phb ; Called via JSL
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phk
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plb
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phd ; save the direct page register
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sta l_addr ; save this value (will go into D-reg later)
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clc
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adc #L_CHAR_COUNT*CHAR_WIDTH ; advance past the left characters
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sta m_addr ; this is the DP for the TSB slam
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lda l_addr
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clc
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adc ScreenWidth
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sec
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sbc #{R_CHAR_COUNT*CHAR_WIDTH}
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sta r_addr ; this is the DP for the right side
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; Calculate the TSB slam entry point
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sec
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sbc m_addr ; calculate the number of words between the two ends
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and #$FFFE
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pha
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lda #m_end
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sec
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sbc 1,s
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sta m_patch+1
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pla
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sei
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_R1W1
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ldy #8 ; count the line we're on
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ldx #0
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ovrly_loop
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lda r_addr
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tcd ; set the direct page for the right side
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jmp r_ovrly ; render that line
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r_ovrly_rtn
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lda m_addr
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tcd ; set the direct page for the slam in the middle
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lda #0 ; set to zero for TSB slam
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m_patch jmp $0000 ; jump into the slam field
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m_ovrly_rtn
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lda l_addr ; set the direct page for the left side
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tcd
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jmp l_ovrly
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l_ovrly_rtn
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clc
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tdc
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adc #160 ; advance to the next screen line
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sta l_addr
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adc #{L_CHAR_COUNT*CHAR_WIDTH}
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sta m_addr
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lda r_addr
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adc #160
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sta r_addr
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txa
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adc #OVRLY_SPAN
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tax
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dey
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bne ovrly_loop
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_R0W0
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cli
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:exit
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pld ; restore the direct page and bank and return
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plb
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rtl
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l_addr ds 2
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m_addr ds 2
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r_addr ds 2
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r_ovrly
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]idx equ 0
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lup R_CHAR_COUNT
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lda ]idx
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and r_line+MASK_OFFSET+]idx,x
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ora r_line+]idx,x
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sta ]idx
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lda ]idx+2
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and r_line+MASK_OFFSET+]idx+2,x
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ora r_line+]idx+2,x
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sta ]idx+2
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]idx equ ]idx+4
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--^
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jmp r_ovrly_rtn ; In R1W1, so can't use the stack
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l_ovrly
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]idx equ 0
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lup L_CHAR_COUNT
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lda ]idx
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and l_line+MASK_OFFSET+]idx,x
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ora l_line+]idx,x
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sta ]idx
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lda ]idx+2
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and l_line+MASK_OFFSET+]idx+2,x
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ora l_line+]idx+2,x
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sta ]idx+2
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]idx equ ]idx+4
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--^
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jmp l_ovrly_rtn
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; Single TSB slam
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m_line
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]idx equ $9E
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lup 80 ; 80 words max for a full-width screen
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tsb ]idx
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]idx equ ]idx-2
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--^
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m_end
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jmp m_ovrly_rtn
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; Draw a character (tile) into a location of the overlay
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;
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; A = Tile ID
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; Y = overlay address location
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tiledata EXT
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_DCOut rts
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_DrawChar
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cmp #'0'
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bcc _DCOut
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cmp #'Z'+1
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bcs _DCOut
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sec
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sbc #'0'
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clc
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adc #CHAR_TILE_BASE
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jsl GetTileAddr
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tax
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]idx equ 0
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lup 8
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ldal tiledata+32+{]idx*4},x
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sta: {]idx*OVRLY_SPAN}+MASK_OFFSET,y
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ldal tiledata+{]idx*4},x
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sta: {]idx*OVRLY_SPAN},y
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ldal tiledata+32+{]idx*4}+2,x
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sta: {]idx*OVRLY_SPAN}+MASK_OFFSET+2,y
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ldal tiledata+{]idx*4}+2,x
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sta: {]idx*OVRLY_SPAN}+2,y
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]idx equ ]idx+1
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--^
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rts |