C API Bindings - Fern UI Framework

The Fern C API provides a C-compatible interface for using Fern in C projects and WebAssembly applications. This API is designed for simplicity and ease of integration with C codebases and web environments.

Core Types

Point

typedef struct Point {
    int x;
    int y;
} Point;

Represents a 2D point with integer coordinates.

Point Point_create(int x, int y);

FernCanvas

typedef struct FernCanvas {
    uint32_t* pixels;
    size_t height;
    size_t width;
} FernCanvas;

Represents the canvas pixel buffer.

InputState

typedef struct InputState {
    int mouse_x;
    int mouse_y;
    int mouse_down;
    int mouse_clicked;
} InputState;

Contains current mouse input state.

ButtonConfig

typedef struct ButtonConfig {
    int x;
    int y;
    int width;
    int height;
    uint32_t normal_color;
    uint32_t hover_color;
    uint32_t press_color;
    const char* label;
    int text_scale;
    uint32_t text_color;
    ButtonCallback on_click;
} ButtonConfig;

Configuration for button widgets.

GradientStop

typedef struct GradientStop {
    uint32_t color;
    float position;  // 0-1
} GradientStop;

Defines a color stop in a gradient.

LinearGradient

typedef struct LinearGradient {
    GradientStop* stops;
    int stop_count;
    int direction;  // 0 = horizontal, 1 = vertical
} LinearGradient;

Defines a linear gradient.

Color Constants

#define Colors_green  0xFF00FF00
#define Colors_blue   0xFF0000FF
#define Colors_red    0xFFFF0000
#define Colors_gray   0xFF202020
#define Colors_black  0xFF000000
#define Colors_white  0xFFFFFFFF

Gradient Constants

#define GRADIENT_HORIZONTAL 0
#define GRADIENT_VERTICAL   1

Initialization

fern_init_wasm()

void fern_init_wasm(uint32_t* pixel_buffer, size_t height, size_t width)

Initializes the Fern framework for WebAssembly.

pixel_buffer

uint32_t*

required

Pointer to the pixel buffer array

height

size_t

required

Canvas height in pixels

width

size_t

required

Canvas width in pixels

runApp()

void runApp(FernCanvas canvas)

Initializes and runs the Fern application.

canvas

FernCanvas

required

Canvas structure containing pixel buffer and dimensions

Drawing Functions

ffill()

void ffill(uint32_t* pixels, size_t height, size_t width, uint32_t color)

Fills the entire canvas with a solid color.

pixels

uint32_t*

required

Pixel buffer array

height

size_t

required

Canvas height

width

size_t

required

Canvas width

color

uint32_t

required

Fill color (0xAABBGGRR format)

frect()

void frect(uint32_t* pixels, size_t height, size_t width, uint32_t color, 
          size_t x, size_t y, size_t w, size_t h)

Draws a filled rectangle.

pixels

uint32_t*

required

Pixel buffer array

height

size_t

required

Canvas height

width

size_t

required

Canvas width

color

uint32_t

required

Rectangle color

size_t

required

Rectangle x position

size_t

required

Rectangle y position

size_t

required

Rectangle width

size_t

required

Rectangle height

fcircle()

void fcircle(uint32_t* pixels, size_t height, size_t width, uint32_t color, 
            size_t cx, size_t cy, size_t r)

Draws a filled circle.

pixels

uint32_t*

required

Pixel buffer array

height

size_t

required

Canvas height

width

size_t

required

Canvas width

color

uint32_t

required

Circle color

size_t

required

Circle center x

size_t

required

Circle center y

size_t

required

Circle radius

fline()

void fline(uint32_t* pixels, size_t height, size_t width, uint32_t color, 
          int x1, int y1, int x2, int y2, int thickness)

Draws a line between two points using Bresenham’s algorithm.

pixels

uint32_t*

required

Pixel buffer array

height

size_t

required

Canvas height

width

size_t

required

Canvas width

color

uint32_t

required

Line color

int

required

Start point x

int

required

Start point y

int

required

End point x

int

required

End point y

thickness

int

required

Line thickness in pixels

Text Rendering

fchar()

void fchar(uint32_t* pixels, int width, int height, char c, int x, int y, int scale, uint32_t color)

Renders a single character.

pixels

uint32_t*

required

Pixel buffer array

width

int

required

Canvas width

height

int

required

Canvas height

char

required

Character to render (A-Z, 0-9)

int

required

X position

int

required

Y position

scale

int

required

Character scale factor

color

uint32_t

required

Text color

ftext()

void ftext(uint32_t* pixels, int width, int height, const char* text, int x, int y, int scale, uint32_t color)

Renders a text string.

pixels

uint32_t*

required

Pixel buffer array

width

int

required

Canvas width

height

int

required

Canvas height

text

const char*

required

Text string to render

int

required

X position

int

required

Y position

scale

int

required

Text scale factor

color

uint32_t

required

Text color

Container()

void Container(uint32_t color, int x, int y, int width, int height)

Draws a rectangular container.

CenteredContainer()

void CenteredContainer(int width, int height, uint32_t color)

Draws a centered rectangular container.

CircleWidget()

void CircleWidget(int radius, Point position, uint32_t color)

Draws a circle widget.

LineWidget()

void LineWidget(Point start, Point end, int thickness, uint32_t color)

Draws a line widget.

TextWidget()

void TextWidget(Point start, const char* text, int scale, uint32_t color)

Draws a text widget.

ButtonWidget()

void ButtonWidget(ButtonConfig config)

Draws an interactive button widget.

LinearGradientContainer()

void LinearGradientContainer(int x, int y, int width, int height, LinearGradient gradient)

Draws a container with a linear gradient.

Color Functions

fblend_color()

uint32_t fblend_color(uint32_t color1, uint32_t color2, float t)

Blends two colors together.

color1

uint32_t

required

First color

color2

uint32_t

required

Second color

float

required

Blend factor (0.0 to 1.0)

return

uint32_t

Blended color

gradient_color_at()

uint32_t gradient_color_at(LinearGradient grad, float position)

Calculates the color at a position in a gradient.

grad

LinearGradient

required

Gradient definition

position

float

required

Position in gradient (0.0 to 1.0)

return

uint32_t

Color at the position

Render Loop

fern_set_draw_callback()

void fern_set_draw_callback(FernDrawCallback callback)

Sets the draw callback function for the render loop.

callback

FernDrawCallback

required

Function pointer to draw callback

fern_start_render_loop()

void fern_start_render_loop(void)

Starts the main render loop (WebAssembly only).

Input Functions

update_mouse_position()

void update_mouse_position(int x, int y)

Updates the mouse position (called by event handlers).

update_mouse_button()

void update_mouse_button(int down)

Updates the mouse button state (called by event handlers).

reset_input_events()

void reset_input_events(void)

Resets frame-specific input events.

Utility Functions

fernPrintf()

void fernPrintf(const char* string)

Prints a debug message to console.

string

const char*

required

Message to print

Example Usage

#include <stdint.h>

// Create canvas
uint32_t pixels[800 * 600];
FernCanvas canvas = { pixels, 600, 800 };

// Draw callback
void draw() {
    ffill(canvas.pixels, canvas.height, canvas.width, Colors_gray);
    
    Container(Colors_blue, 50, 50, 200, 100);
    CircleWidget(25, Point_create(150, 100), Colors_red);
    TextWidget(Point_create(100, 200), "HELLO", 2, Colors_white);
}

int main() {
    runApp(canvas);
    fern_set_draw_callback(draw);
    fern_start_render_loop();
    return 0;
}

Core

Graphics

Font System

C API

​Core Types

​Point

​FernCanvas

​InputState

​ButtonConfig

​GradientStop

​LinearGradient

​Color Constants

​Gradient Constants

​Initialization

​fern_init_wasm()

​runApp()

​Drawing Functions

​ffill()

​frect()

​fcircle()

​fline()

​Text Rendering

​fchar()

​ftext()

​Widget Functions

​Container()

​CenteredContainer()

​CircleWidget()

​LineWidget()

​TextWidget()

​ButtonWidget()

​LinearGradientContainer()

​Color Functions

​fblend_color()

​gradient_color_at()

​Render Loop

​fern_set_draw_callback()

​fern_start_render_loop()

​Input Functions

​update_mouse_position()

​update_mouse_button()

​reset_input_events()

​Utility Functions

​fernPrintf()

​Example Usage

Build docs developers (and LLMs) love

Core Types

Point

FernCanvas

InputState

ButtonConfig

GradientStop

LinearGradient

Color Constants

Gradient Constants

Initialization

fern_init_wasm()

runApp()

Drawing Functions

ffill()

frect()

fcircle()

fline()

Text Rendering

fchar()

ftext()

Widget Functions

Container()

CenteredContainer()

CircleWidget()

LineWidget()

TextWidget()

ButtonWidget()

LinearGradientContainer()

Color Functions

fblend_color()

gradient_color_at()

Render Loop

fern_set_draw_callback()

fern_start_render_loop()

Input Functions

update_mouse_position()

update_mouse_button()

reset_input_events()

Utility Functions

fernPrintf()

Example Usage