xen32os/xenrom/text.asm

font_table: #include_bin "data/font_table.dat"
font_data: #include_bin "data/font_data.dat"
; defines FONT_SIZE and FONT_LINE_HEIGHT
#include "data/font_data.inc"


; input:
;   r0: pointer to frame buffer
;   r1: frame buffer width
;   r2: pointer to string to draw
;   r3: x coordinate to draw at
;   r4: y coordinate to draw at
;   r5: text box left
;   r6: text box right
;   r7: text box bottom
;   r30: text delay (ms, blocking)
;   r31: text color
; returns:
;   r0, r1, r5, r6, r7, r30, r31 kept
;   r2: pointer to last char drawn
;   r3: x coordinate to next char to draw
;   r4: y coordinate to next char to draw

draw_str_at:
    ; store char pointer in r8
    mov r8, r2

  draw_str_at_loop:
    cmp r30, 0
    ifnz call font_sleep

    ; r2: current char
    movz.8 r2, [r8]
    cmp r2, 0 ; check for null terminator
    ifz jmp draw_str_at_loop_end

    ; check for newline
    cmp r2, 10
    ifz jmp draw_str_at_newline

    ; r9: char entry
    mov r9, r2
    mul r9, 7
    add r9, font_table
    ; r10: width, r11: end x
    movz.8 r10, [r9]
    mov r11, r3
    add r11, r10

    ; are we after the edge?
    cmp r11, r6
    iflt jmp draw_str_at_loop_draw
    ; if we have a space, don't reset
    cmp r2, 32
    ifz jmp draw_str_at_loop_draw

  draw_str_at_linebreak:

    mov r3, r5 ; reset x
    ; update end x
    mov r11, r5
    add r11, r10
    ; step to next line, check if we've overrun the box
    add r4, FONT_LINE_HEIGHT
    cmp r4, r7
    ifgteq jmp draw_str_at_loop_end

  draw_str_at_loop_draw:
    push r0
    push r1
    push r2
    push r3
    push r4
    call draw_char_at
    pop r4
    pop r3
    pop r2
    pop r1
    pop r0

  draw_str_at_spaceskip:
    inc r8 ; update string index
    mov r3, r11 ; update x coordinate
    add r3, FONT_SIZE ; padding
    jmp draw_str_at_loop

  draw_str_at_newline:
    inc r8 ; update string index
    mov r3, r5 ; reset x
    ; step to next line, check if we've overrur the box
    add r4, FONT_LINE_HEIGHT
    cmp r4, r7
    ifgteq jmp draw_str_at_loop_end
    jmp draw_str_at_loop

  draw_str_at_loop_end:

    ; restore char pointer into r2
    mov r2, r8

    ret


; input:
;   r0: pointer to frame buffer
;   r1: frame buffer width
;   r2: char to draw
;   r3: x coordinate to draw at
;   r4: y coordinate to draw at
;   r31: color
; returns:
;   nothing

draw_char_at:
    push r5
    push r6
    push r7
    push r8
    push r9
    ; r5: width
    ; r7: baseline
    ; r8: char data pointer
    ; r9: number of pixels to draw

    mul r2, 7 ; size of char
    add r2, font_table

    movz.8 r5, [r2]
    inc r2
    movz.8 r9, [r2]
    mul r9, r5

    inc r2
    movz.8 r7, [r2]
    inc r2
    mov r8, [r2]
    add r8, font_data

    ; adjust y for baseline
    sub r4, r7

    ; calculate init framebuffer address into r4
    mul r4, r1
    add r4, r3
    mul r4, 4
    add r4, r0

    ; r6: x counter in glyph
    ; r9: countdown
    mov r6, 0
  draw_char_at_loop:
    cmp r9, 0 ; zero terminator
    ifz jmp draw_char_at_loop_done

    cmp.8 [r8], 0
    ifnz mov [r4], r31

    inc r8 ; advance glyph data pointer
    dec r9 ; lower count
    add r4, 4 ; advance screen pointer
    inc r6 ; advance x counter
    cmp r6, r5 ; are we at the end of the glyph line?
    ifnz jmp draw_char_at_loop
    ; move screen pointer down one (x4 for 4 bytes per pixel)
    add r4, r1
    add r4, r1
    add r4, r1
    add r4, r1
    sub r4, r5
    sub r4, r5
    sub r4, r5
    sub r4, r5
    mov r6, 0

    jmp draw_char_at_loop

  draw_char_at_loop_done:

    pop r9
    pop r8
    pop r7
    pop r6
    pop r5

    ret

; input
;   r30: time to sleep (ms)
font_sleep:
    push r0
    push r1
    ; r0: end time
    ; r1: current time
    in r0, 0x8000_0706 ; RTC uptime (ms)
    add r0, r30
  font_sleep_busyloop:
    in r1, 0x8000_0706
    cmp r1, r0
    iflt jmp font_sleep_busyloop

    pop r1
    pop r0
    ret