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Print string using a custom font

This ROM displays "Hello world!" using the print_string routine and a custom font.

custom font

First we need to convert the font into the native tile format. We'll use the encode_gfx tool.

The image for the custom font contains 256 tiles (16 by 16) mapping each ASCII character.

{
    "tile": [
        { "name": "font.bin", "x":0, "y":0, "w":16, "h":16 }
    ],
    "palette": [
        { "name": "palette.bin", "start": 0, "count": 1 }
    ]
}

In order to prevent HuDK from using the system font, we will have to define some prepocessor variables before any HuDK include file. Namely

  • HUDK_USE_CUSTOM_FONT in order to prevent HuDK from inclusing the default font.
  • FONT_8x8_COUNTthe number of characters in the font.
  • FONT_ASCII_FIRST the ASCII code of the first character.
  • FONT_ASCII_LAST the ASCII code of the last character.
  • FONT_DIGIT_INDEX the index of the first digit (0).
  • FONT_UPPER_CASE_INDEX the index of the first upper case character (A).
  • FONT_LOWER_CASE_INDEX the index of the first lower case character (a).

In our case we will have:

asmC
FONT_8x8_COUNT=$1ff
FONT_ASCII_FIRST=$00
FONT_ASCII_LAST =$9e
FONT_DIGIT_INDEX=$30
FONT_UPPER_CASE_INDEX=$41
FONT_LOWER_CASE_INDEX=$61
 
#define FONT_8x8_COUNT 0x1ff
#define FONT_ASCII_FIRST 0x00
#define FONT_ASCII_LAST 0x9e
#define FONT_DIGIT_INDEX 0x30
#define FONT_UPPER_CASE_INDEX 0x41
#define FONT_LOWER_CASE_INDEX 0x61

Next, we will have to copy the palette to the VCE using the vce_load_palette routine, and the tiles to VRAM using vdc_load_data.

asmC
    ; load font palette
    stb    #bank(palette_bin), <_bl
    stw    #palette_bin, <_si
    jsr    map_data
    cla
    ldy    #1
    jsr    vce_load_palette

    ; load font gfx
    stb    #bank(font_bin), <_bl
    stw    #font_bin, <_si
    stw    #(VDC_DEFAULT_TILE_ADDR), <_di
    stw    #4096, <_cx
    jsr    vdc_load_data
 
// load font palette
vce_load_palette(0, 1, palette);

// load font gfx
vdc_load_data(VDC_DEFAULT_TILE_ADDR, font_bin, 4096);

We then have to tell the print routines where the font is located in VRAM and which palette to use.

asmC
    ; set font VRAM address
    ldx    #low(VDC_DEFAULT_TILE_ADDR)
    lda    #high(VDC_DEFAULT_TILE_ADDR)
    jsr    font_set_addr

    ; set font palette
    lda    #$00
    jsr    font_set_pal
 
// set font VRAM address
font_set_addr(VDC_DEFAULT_TILE_ADDR);

// set font palette
font_set_pal(0);

Now, any call to the print routines will use the newly defined custom font.

screenshot