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
firebrickolive drabdodger bluewith 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
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