Canvas

The canvas widget is the basic widget used to drawing graphics in nanovg.

Warning

Sufficient memory is needed to open a framebuffer.

Usage

Creat Canvas

gui_canvas_create() creates a canvas.

Add Callback Function

gui_canvas_set_canvas_cb() sets the callback function for drawing specific shapes.

Example

Rounded Rectangle

A simple example of drawing three rounded rectangles of different colors.

• Three color refer to Colors’ RGB Data.

• firebrick

• olive drab

• dodger blue with 100 value opacity

#include "gui_canvas.h"
static void canvas_cb(gui_canvas_t *canvas)
{
    nvgRoundedRect(canvas->vg, 10, 10, 348, 200, 30);
    nvgFillColor(canvas->vg, nvgRGB(178,34,34));
    nvgFill(canvas->vg);
    nvgBeginPath(canvas->vg);
    nvgRoundedRect(canvas->vg, 10, 220, 348, 200, 30);
    nvgFillColor(canvas->vg, nvgRGB(107,142,35));
    nvgFill(canvas->vg);
    nvgBeginPath(canvas->vg);
    nvgRoundedRect(canvas->vg, 110, 125, 148, 200, 30);
    nvgFillColor(canvas->vg, nvgRGBA(30,144,255, 100));
    nvgFill(canvas->vg);
}
static void app_ui_design(gui_app_t *app)
{
    gui_canvas_t *canvas = gui_canvas_create(&(app->screen), "canvas", 0, 0, 0, 368, 448);
    gui_canvas_set_canvas_cb(canvas, canvas_cb);
}

Arc Animation

An example of drawing an arc animation. arc_cb will be triggered every frame.

#include "math.h"
#include "gui_canvas.h"
static void arc_cb(gui_canvas_t *canvas)
{
    static float  progress;
    progress +=0.01;
    nvgArc(canvas->vg, 368/2, 448/2, 150, 0, 3.14*(sinf(progress)+1), NVG_CCW);
    nvgStrokeWidth(canvas->vg, 20);
    nvgStrokeColor(canvas->vg, nvgRGB(178,34,34));
    nvgStroke(canvas->vg);
}
static void app_ui_design(gui_app_t *app)
{
    gui_canvas_t *canvas = gui_canvas_create(&(app->screen), "canvas", 0, 0, 0, 368, 448);
    gui_canvas_set_canvas_cb(canvas, arc_cb);
}

API

Nanovg API

Please refer to

Nanovg Introduction

Nanovg Github

RealGUI API

Defines

GUI_CANVAS_OUTPUT_PNG 1

GUI_CANVAS_OUTPUT_JPG 2

GUI_CANVAS_OUTPUT_RGBA 3

GUI_CANVAS_OUTPUT_RGB565 4

Typedefs

typedef void (*gui_canvas_render_function)(NVGcontext *vg)

Functions

gui_canvas_t *gui_canvas_create(void *parent, const char *name, void *addr, int16_t x, int16_t y, int16_t w, int16_t h)

Create a canvas widget used to draw graphics in NanoVG.

Parameters:

• parent – The father widget nested in.

• name – This widget’s canvas name.

• addr – Address.

• x – The X-axis coordinate relative to parent widget.

• y – The Y-axis coordinate relative to parent widget.

• w – Width.

• h – Height.

Returns:

Return the canvas widget pointer.

void gui_canvas_set_canvas_cb(gui_canvas_t *this_widget, void (*cb)(gui_canvas_t *this_widget))

Set the callback function for drawing specific shapes.

Parameters:

• this_widget – This widget pointer.

• cb – The callback function for drawing specific shapes.

const uint8_t *gui_canvas_output(int output_format, bool compression, int image_width, int image_height, gui_canvas_render_function renderer)

Render a canvas and output it in the specified format.

Parameters:

• output_format – The format of the output image.

• compression – Whether to apply compression to the output.

• image_width – The width of the output image.

• image_height – The height of the output image.

• renderer – A function pointer to the rendering function.

Returns:

Return a pointer to the buffer containing the output image data.

void gui_canvas_output_buffer(int format, bool compression, int image_width, int image_height, gui_canvas_render_function renderer, uint8_t *target_buffer)

Render a canvas and output the result to a target buffer in the specified format.

Parameters:

• format – The format of the output image.

• compression – Whether to apply compression to the output.

• image_width – The width of the output image.

• image_height – The height of the output image.

• renderer – A function pointer to the rendering function.

• target_buffer – A pointer to the buffer where the rendered image data will be written.

NVGcontext *gui_canvas_output_buffer_blank(int format, bool compression, int image_width, int image_height, uint8_t *target_buffer)

Initialize a blank output buffer for the canvas.

Parameters:

• format – The format of the output buffer.

• compression – Boolean flag indicating whether compression should be used.

• image_width – The width of the image.

• image_height – The height of the image.

• target_buffer – Pointer to the target buffer where the output will be stored.

Returns:

Return a pointer to the initialized NanoVG context.

void gui_canvas_output_buffer_blank_close(NVGcontext *vg)

Close the canvas and free resources.

Parameters:

vg – Pointer to the NanoVG context to be closed.

struct gui_canvas_t

canvas structure

Public Members

gui_obj_t base

NVGcontext *vg

void (*nanovg_canvas_cb)(struct gui_canvas *this_widget)

uint8_t checksum

uint8_t render