canvas

The canvas widget is the basic widget used to drawing graphics in nanovg.Limitations: Sufficient memory is needed to open a framebuffer.

Usage

Creat a canvas

gui_canvas_create(parent, name, addr, x, y, w, h) creates a canvas. This addr can be a null pointer.

Add callback function

gui_canvas_set_canvas_cb(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

Vector graphics api

Please refer to

• nanovg-introduction
• nanovg github

GUI widget api

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 drawing graphics in nanovg.

Parameters:

• parent – the father widget nested in.

• name – this_widget canvas widget’s name.

• addr –

• x – the X-axis coordinate relative to parent widget

• y – the Y-axis coordinate relative to parent widget

• w – width

• h – height

Returns:

gui_canvas_t*

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 widget pointer

• cb – the callback function for drawing specific shapes

struct gui_canvas_t

#include <gui_canvas.h>

canvas structure

Public Members

gui_obj_t base

NVGcontext *vg

void (*nanovg_canvas_cb)(struct gui_canvas *this_widget)