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sokol_debugtext.h - simple ASCII debug text rendering on top of sokol_gfx.h

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Do this: #define SOKOL_IMPL or #define SOKOL_DEBUGTEXT_IMPL before you include this file in one C or C++ file to create the implementation.

The following defines are used by the implementation to select the platform-specific embedded shader code (these are the same defines as used by sokol_gfx.h and sokol_app.h):


...optionally provide the following macros to override defaults:

SOKOL_VSNPRINTF - the function name of an alternative vsnprintf() function (default: vsnprintf) SOKOL_ASSERT(c) - your own assert macro (default: assert(c)) SOKOL_DEBUGTEXT_API_DECL - public function declaration prefix (default: extern) SOKOL_API_DECL - same as SOKOL_DEBUGTEXT_API_DECL SOKOL_API_IMPL - public function implementation prefix (default: -) SOKOL_UNREACHABLE() - a guard macro for unreachable code (default: assert(false))

If sokol_debugtext.h is compiled as a DLL, define the following before including the declaration or implementation:


On Windows, SOKOL_DLL will define SOKOL_DEBUGTEXT_API_DECL as __declspec(dllexport) or __declspec(dllimport) as needed.

Include the following headers before including sokol_debugtext.h:



  • renders 8-bit ASCII text as fixed-size 8x8 pixel characters
  • comes with 6 embedded 8-bit home computer fonts (each taking up 2 KBytes)
  • easily plug in your own fonts
  • create multiple contexts for rendering text in different layers or render passes


--- to initialize sokol-debugtext, call sdtx_setup() after initializing sokol-gfx:

    sdtx_setup(&(sdtx_desc_t){ ... });

--- configure sokol-debugtext by populating the sdtx_desc_t struct:

.context_pool_size (default: 8)
    The max number of text contexts that can be created.

.printf_buf_size (default: 4096)
    The size of the internal text formatting buffer used by
    sdtx_printf() and sdtx_vprintf().

.fonts (default: none)
    An array of sdtx_font_desc_t structs used to configure the
    fonts that can be used for rendering. To use all builtin
    fonts call sdtx_setup() like this (in C99):

        .fonts = {
            [0] = sdtx_font_kc853(),
            [1] = sdtx_font_kc854(),
            [2] = sdtx_font_z1013(),
            [3] = sdtx_font_cpc(),
            [4] = sdtx_font_c64(),
            [5] = sdtx_font_oric()

    For documentation on how to use you own font data, search
    below for "USING YOUR OWN FONT DATA".

    The setup parameters for the default text context. This will
    be active right after sdtx_setup(), or when calling

    .max_commands (default: 4096)
        The max number of render commands that can be recorded
        into the internal command buffer. This directly translates
        to the number of render layer changes in a single frame.

    .char_buf_size (default: 4096)
        The number of characters that can be rendered per frame in this
        context, defines the size of an internal fixed-size vertex
        buffer.  Any additional characters will be silently ignored.

    .canvas_width (default: 640)
    .canvas_height (default: 480)
        The 'virtual canvas size' in pixels. This defines how big
        characters will be rendered relative to the default framebuffer
        dimensions. Each character occupies a grid of 8x8 'virtual canvas
        pixels' (so a virtual canvas size of 640x480 means that 80x60 characters
        fit on the screen). For rendering in a resizeable window, you
        should dynamically update the canvas size in each frame by
        calling sdtx_canvas(w, h).

    .tab_width (default: 4)
        The width of a tab character in number of character cells.

    .color_format (default: 0)
    .depth_format (default: 0)
    .sample_count (default: 0)
        The pixel format description for the default context needed
        for creating the context's sg_pipeline object. When
        rendering to the default framebuffer you can leave those
        zero-initialized, in this case the proper values will be
        filled in by sokol-gfx. You only need to provide non-default
        values here when rendering to render targets with different
        pixel format attributes than the default framebuffer.

--- Before starting to render text, optionally call sdtx_canvas() to dynamically resize the virtual canvas. This is recommended when rendering to a resizeable window. The virtual canvas size can also be used to scale text in relation to the display resolution.

Examples when using sokol-app:

- to render characters at 8x8 'physical pixels':

    sdtx_canvas(sapp_width(), sapp_height());

- to render characters at 16x16 physical pixels:

    sdtx_canvas(sapp_width()/2.0f, sapp_heigth()/2.0f);

Do *not* use integer math here, since this will not look nice
when the render target size isn't divisible by 2.

--- Optionally define the origin for the character grid with:

    sdtx_origin(x, y);

The provided coordinates are in character grid cells, not in
virtual canvas pixels. E.g. to set the origin to 2 character tiles
from the left and top border:

    sdtx_origin(2, 2);

You can define fractions, e.g. to start rendering half
a character tile from the top-left corner:

    sdtx_origin(0.5f, 0.5f);

--- Optionally set a different font by calling:


sokol-debugtext provides 8 font slots which can be populated
with the builtin fonts or with user-provided font data, so
'font_index' must be a number from 0 to 7.

--- Position the text cursor with one of the following calls. All arguments are in character grid cells as floats and relative to the origin defined with sdtx_origin():

    sdtx_pos(x, y)      - sets absolute cursor position
    sdtx_pos_x(x)       - only set absolute x cursor position
    sdtx_pos_y(y)       - only set absolute y cursor position

    sdtx_move(x, y)     - move cursor relative in x and y direction
    sdtx_move_x(x)      - move cursor relative only in x direction
    sdtx_move_y(y)      - move cursor relative only in y direction

    sdtx_crlf()         - set cursor to beginning of next line
                          (same as sdtx_pos_x(0) + sdtx_move_y(1))
    sdtx_home()         - resets the cursor to the origin
                          (same as sdtx_pos(0, 0))

--- Set a new text color with any of the following functions:

    sdtx_color3b(r, g, b)       - RGB 0..255, A=255
    sdtx_color3f(r, g, b)       - RGB 0.0f..1.0f, A=1.0f
    sdtx_color4b(r, g, b, a)    - RGBA 0..255
    sdtx_color4f(r, g, b, a)    - RGBA 0.0f..1.0f
    sdtx_color1i(uint32_t rgba) - ABGR (0xAABBGGRR)

--- Output 8-bit ASCII text with the following functions:

    sdtx_putc(c)             - output a single character

    sdtx_puts(str)           - output a null-terminated C string, note that
                               this will *not* append a newline (so it behaves
                               differently than the CRT's puts() function)

    sdtx_putr(str, len)     - 'put range' output the first 'len' characters of
                               a C string or until the zero character is encountered

    sdtx_printf(fmt, ...)   - output with printf-formatting, note that you
                              can inject your own printf-compatible function
                              by overriding the SOKOL_VSNPRINTF define before
                              including the implementation

    sdtx_vprintf(fmt, args) - same as sdtx_printf() but with the arguments
                              provided in a va_list

- Note that the text will not yet be rendered, only recorded for rendering
  at a later time, the actual rendering happens when sdtx_draw() is called
  inside a sokol-gfx render pass.
- This means also you can output text anywhere in the frame, it doesn't
  have to be inside a render pass.
- Note that character codes <32 are reserved as control characters
  and won't render anything. Currently only the following control
  characters are implemented:

    \r  - carriage return (same as sdtx_pos_x(0))
    \n  - carriage return + line feed (same as stdx_crlf())
    \t  - a tab character

--- You can 'record' text into render layers, this allows to mix/interleave sokol-debugtext rendering with other rendering operations inside sokol-gfx render passes. To start recording text into a different render layer, call:

    sdtx_layer(int layer_id)

...outside a sokol-gfx render pass.

--- finally, from within a sokol-gfx render pass, call:


...for non-layered rendering, or to draw a specific layer:

    sdtx_draw_layer(int layer_id)

NOTE that sdtx_draw() is equivalent to:

    sdtx_draw_layer(0) sdtx_draw() will *NOT* render all text layers, instead it will
only render the 'default layer' 0.

--- at the end of a frame (defined by the call to sg_commit()), sokol-debugtext will rewind all contexts:

    - the internal vertex index is set to 0
    - the internal command index is set to 0
    - the current layer id is set to 0
    - the current font is set to 0
    - the cursor position is reset


Use multiple text contexts if you need to render debug text in different sokol-gfx render passes, or want to render text to different layers in the same render pass, each with its own set of parameters.

To create a new text context call:

sdtx_context ctx = sdtx_make_context(&(sdtx_context_desc_t){ ... });

The creation parameters in the sdtx_context_desc_t struct are the same as already described above in the sdtx_setup() function:

.char_buf_size      -- max number of characters rendered in one frame, default: 4096
.canvas_width       -- the initial virtual canvas width, default: 640
.canvas_height      -- the initial virtual canvas height, default: 400
.tab_width          -- tab width in number of characters, default: 4
.color_format       -- color pixel format of target render pass
.depth_format       -- depth pixel format of target render pass
.sample_count       -- MSAA sample count of target render pass

To make a new context the active context, call:


...and after that call the text output functions as described above, and finally, inside a sokol-gfx render pass, call sdtx_draw() to actually render the text for this context.

A context keeps track of the following parameters:

- the active font
- the virtual canvas size
- the origin position
- the current cursor position
- the current tab width
- the current color
- and the current layer-id

You can get the currently active context with:


To make the default context current, call sdtx_set_context() with the special SDTX_DEFAULT_CONTEXT handle:


Alternatively, use the function sdtx_default_context() to get the default context handle:


To destroy a context, call:


If a context is set as active that no longer exists, all sokol-debugtext functions that require an active context will silently fail.

You can directly draw the recorded text in a specific context without setting the active context:

sdtx_context_draw_layer(ctx, layer_id)


Instead of the built-in fonts you can also plug your own font data into sokol-debugtext by providing one or several sdtx_font_desc_t structures in the sdtx_setup call.

For instance to use a built-in font at slot 0, and a user-font at font slot 1, the sdtx_setup() call might look like this:

    .fonts = {
        [0] = sdtx_font_kc853(),
        [1] = {
            .data = {
                .ptr = my_font_data,
                .size = sizeof(my_font_data)
            .first_char = ...,
            .last_char = ...

Where 'my_font_data' is a byte array where every character is described by 8 bytes arranged like this:

7 6 5 4 3 2 1 0
. . . X X . . .     byte 0: 0x18
. . X X X X . .     byte 1: 0x3C
. X X . . X X .     byte 2: 0x66
. X X . . X X .     byte 3: 0x66
. X X X X X X .     byte 4: 0x7E
. X X . . X X .     byte 5: 0x66
. X X . . X X .     byte 6: 0x66
. . . . . . . .     byte 7: 0x00

A complete font consists of 256 characters, resulting in 2048 bytes for the font data array (but note that the character codes 0..31 will never be rendered).

If you provide such a complete font data array, you can drop the .first_char and .last_char initialization parameters since those default to 0 and 255, note that you can also use the SDTX_RANGE() helper macro to build the .data item:

    .fonts = {
        [0] = sdtx_font_kc853(),
        [1] = {
            .data = SDTX_RANGE(my_font_data)

If the font doesn't define all 256 character tiles, or you don't need an entire 256-character font and want to save a couple of bytes, use the .first_char and .last_char initialization parameters to define a sub-range. For instance if the font only contains the characters between the Space (ASCII code 32) and uppercase character 'Z' (ASCII code 90):

    .fonts = {
        [0] = sdtx_font_kc853(),
        [1] = {
            .data = SDTX_RANGE(my_font_data),
            .first_char = 32,       // could also write ' '
            .last_char = 90         // could also write 'Z'

Character tiles that haven't been defined in the font will be rendered as a solid 8x8 quad.


You can override the memory allocation functions at initialization time like this:

void* my_alloc(size_t size, void* user_data) {
    return malloc(size);

void my_free(void* ptr, void* user_data) {

        // ...
        .allocator = {
            .alloc = my_alloc,
            .free = my_free,
            .user_data = ...;

If no overrides are provided, malloc and free will be used.


You can override the log function at initialization time like this:

void my_log(const char* message, void* user_data) {
    printf("sdtx says: \s\n", message);

        // ...
        .logger = {
            .log_cb = my_log,
            .user_data = ...,

If no overrides are provided, puts will be used on most platforms. On Android, __android_log_write will be used instead.


zlib/libpng license

Copyright (c) 2020 Andre Weissflog

This software is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.

Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:

1. The origin of this software must not be misrepresented; you must not
claim that you wrote the original software. If you use this software in a
product, an acknowledgment in the product documentation would be
appreciated but is not required.

2. Altered source versions must be plainly marked as such, and must not
be misrepresented as being the original software.

3. This notice may not be removed or altered from any source