render_core.8o

:if KEEP_META_COMMENTS

# Include this file:
# 1. After font metadata definitions
# 2. Before the main body of your program

# Forgiving ifndef-like imports for dependencies.
:end
:unless TERMLIB_COMMON  :include  "common.8o" :end
:unless TERMLIB_DRAWING :include "drawing.8o" :end

###################################################################
###                      Text rendering core                    ###
###################################################################

# This section contains the high-level description of how to render
# text. The character-specific functions are kept in render_impl.8o,
# and can be overridden by defining the following before including
# render_impl.8o:

# 1. A CUSTOM_$FUNC_NAME constant as shown in the file
# 2. The corresponding function

# UI data we'll need
:const GLYPH_WIDTH_PX          4 # Usable glyph area
:const GLYPH_HEIGHT_PX         7 # Usable glyph area
:const GLYPH_TRACKING_PX       1 # Space between the characters
:const LINE_LEADING_PX         1 # Space after lines

:calc  GLYPH_STEP_X_PX         { GLYPH_WIDTH_PX  + GLYPH_TRACKING_PX }
:calc  GLYPH_STEP_Y_PX         { GLYPH_HEIGHT_PX + LINE_LEADING_PX   }

:const GLYPH_DATA_HEIGHT_PX    6 # Standard glyphs have this height
:calc  GLYPH_DATA_LENGTH_BYTES { 2 * GLYPH_DATA_HEIGHT_PX }
:calc  HIGHLIGHT_HEIGHT_PX     { GLYPH_DATA_HEIGHT_PX + 1 }


# Where on screen the current message starts
:alias msg_start_x            v9
:alias msg_start_y            vA

# Current character & text mode
:alias current_byte_index     vB

  #: The current offset into the message.

:alias current_byte_value     vC

  #: The read value of the current byte.

:monitor current_byte_index "%i (decimal)"
:monitor current_byte_value "%c (ascii)"

:alias _msg_reg_0 msg_start_x  :alias _msg_reg_end current_byte_value

# Todo: consider storing the decoded values in memory...
# useful if want to do layout.

  # Universal control characters
  :const CHAR_NULL          0x00  #: End of message

  # "Block" boundaries for text to allow sparse text rendering
  :const CHAR_SPACE         0x20  #: Boundary: start of early block
  :const CHAR_SINGLEQUOTE   0x27  #: Boundary: end of early block
  :const CHAR_A             0x41  #: Boundary: start of letters
  :const CHAR_Z             0x5A  #: Boundary: end of letters

  #: ### Formatting control characters

  :const CHAR_ESCAPE        0x5E  #: The start of an escape sequence.

  #: `^` in text is treated as an escape sequence opener.
  #:
  #: The following Control codes are supported:

  :const CHAR_NEWLINE       0x0A  #: '\n' in text, goes back to the
  :const CHAR_B             0x42  #: Background control code
  :const CHAR_F             0x46  #: Foreground control code
  :const CHAR_D             0x44  #: "Restore defaults"

  :macro _base10 NAME { :calc NAME { CALLS + 0x30 } }

    _base10 CHAR_0
    _base10 CHAR_1
    _base10 CHAR_2
    _base10 CHAR_3
    _base10 CHAR_4
    _base10 CHAR_5
    _base10 CHAR_6
    _base10 CHAR_7
    _base10 CHAR_8
    _base10 CHAR_9

  :const STYLE_PLANE_0    CHAR_0
  :const STYLE_PLANE_1    CHAR_1
  :const STYLE_PLANE_2    CHAR_2
  :const STYLE_PLANE_3    CHAR_3

  # Character constants (check with `& 0x80`; 0b10000000 works too)
  :const END_OF_STRING CHAR_NULL

  # A coherent-ish block of chars values, '0' <= char <= 'Z'
  :const MAINBLOCK_START  CHAR_SINGLEQUOTE
  :const MAINBLOCK_END    CHAR_Z
  :calc  MAINBLOCK_SPAN   { MAINBLOCK_END - MAINBLOCK_START }


: current_msg_state

  #: A struct for persisting the current message state.

  : _current_msg_position
    0x00 # Msg start x
    0x00 # Msg start Y

    0x00 # current_byte_index
    0x00 # current_byte_value

  : _current_msg_position_end


# This has to be a label since we need to use a real
# memory address to persist the state between calls.

: restore-current-msg

  #: Restore the current message pointer to i.

  0xF0 0x00
  : _current_msg_addr
    0x00 0x00

  return


:macro set-current-msg LABEL {

  #: Set the current message to begin showing in a resumable way.
  #:
  #: Args:
  #:   LABEL   : label
  #:     Which null-terminated message to set as active.
  #:
  #: Clobbers:
  #:    v0 - v1
  #:
  #:  Returns : void

    :unpack long LABEL     # Store LABEL into v0, vN; long allows reading higher mem
    i := long _current_msg_addr
    save v0 - v1  # Uses rStart - rEnd form to avoid advancing
}

:macro peek-next-msg-byte vN {

  #: Load the byte at current_byte_index in the current message to vN
  #:
  #: Args:
  #:  vN : vN
  #:    A register containing an offset into the message.
  #: Clobbers:
  #:  i
  #: Returns: u8
  #:  The value of the byte at offset vN from msg start.

  :call restore-current-msg
  i += current_byte_index
  load vN - vN
}

:macro read-msg-byte             vN { current_byte_index += 1  peek-next-msg-byte vN     }

  #: Read the next byte of the message, advancing the current byte index.
  #: Args:
  #:   vN : vN
  #:     Where to read the current byte to.
  #: Updates:
  #:     current_byte_index, i
  #: Returns:
  #:    vN

:macro read-next-byte-as-color   vN { read-msg-byte vN  vN -= CHAR_0 }

  #: Read the next byte of the message as a color, advancing the current byte index.
  #: Args:
  #:   vN : vN
  #:     Where to read the color to.
  #: Updates:
  #:     current_byte_index
  #: Clobbers:
  #:  i
  #: Returns:
  #:    vN


:unless TERMLIB_SHOW_MSG
:const  TERMLIB_SHOW_MSG 1 # Mark this function as implemented

:macro show-msg START_X START_Y MSG_LABEL {

  #: Set the draw cursor to the given X, Y and render a null-terminated message.
  #:
  #: Args:
  #:  START_X  :
  #:      A X position to move the cursor to.
  #:  START_Y :
  #:      A Y position to move the cursor to.
  #:  MSG_LABEL :
  #:      A label-like token which points to a null-terminated message.
  #:
  #: Clobbers:
  #:  i, v0 - v3, vF

  msg_start_x  := START_X   msg_start_y := START_Y
  set-current-msg MSG_LABEL
  :call           _show-msg-render

}

  : _show-msg-render

      #: Render an entire null-terminated message.
      #:
      #: Args:
      #:  msg_start_x : vN
      #:    X position where messages should be shown on the screen
      #:  msg_start_y : vN
      #:    Y position where message should be shown on the screen.
      #: Clobbers:
      #:    v0, current_byte_value, current_byte_index, vF
      #: Updates:
      #:    draw_x, draw_y

      # :breakpoint render

      current_byte_index := 0
      set-draw-coords-to msg_start_x msg_start_y

      loop

        peek-next-msg-byte current_byte_value
        # Exit on end of message, no exceptions
        while current_byte_value != END_OF_STRING

        # :breakpoint decide
        v0 := 0
        if current_byte_value == CHAR_ESCAPE  then v0 := 4 # instructions 2 long
        if current_byte_value == CHAR_NEWLINE then v0 := 8 #

        jump0 _byte_action_table
        : _byte_action_table
          :call render-visible-glyph   jump _byte_action_table_after
          :call handle-control         jump _byte_action_table_after
          :call handle-newline       # jump _byte_action_table_after # Last jump redundant
        : _byte_action_table_after

        : _byte_loop_end
        current_byte_index += 1
      again

  : _show-msg-render-end
  return
:end

:include "default_font_stringmodes.8o"