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Canvas Class

Header: endpoint/Drawing.h
Namespace: GHIElectronics::Endpoint::Drawing

A pixel buffer plus the primitives to draw into it. Pick the size and PixelFormat at Create time; when done, hand Buffer() to whichever device accepts bytes.

class Canvas {};

Example​

auto canvas = Canvas::Create(240, 320, PixelFormat::Rgb565);
canvas.Clear(Color::Black());
canvas.DrawLine(10, 10, 230, 310, Color::Red(), /*thickness=*/2);
canvas.FillCircle(120, 160, 40, Color::Blue());
canvas.DrawText("Hello Endpoint", font, 10, 30, 20, Color::White());
spi.Write(canvas.Buffer().data(), canvas.Buffer().size());

Properties​

Buffer​

std::span<const uint8_t> Buffer() const;

Raw pixel bytes. Length and layout match Width(), Height(), and PixelFormat().

Width​

int Width() const;

Width in pixels.

Height​

int Height() const;

Height in pixels.

PixelFormat​

Drawing::PixelFormat PixelFormat() const;

Pixel layout of Buffer().

Methods​

Create(int width, int height, PixelFormat format)​

static Canvas Create(int width, int height, Drawing::PixelFormat format);

Allocate a new Canvas of the given size and pixel format.

Clear(Color color)​

void Clear(Color color);

Fill the whole buffer with a single color.

SetPixel(int x, int y, Color color)​

void SetPixel(int x, int y, Color color);

Set a single pixel. No-op if (x, y) is outside the canvas.

DrawLine(int x0, int y0, int x1, int y1, Color color, int thickness)​

void DrawLine(int x0, int y0, int x1, int y1, Color color, int thickness = 1);

Bresenham line, honoring thickness by stamping an r-pixel disc at each step.

DrawRectangle(int x, int y, int width, int height, Color color, int thickness)​

void DrawRectangle(int x, int y, int width, int height, Color color, int thickness = 1);

Stroke a rectangle outline.

FillRectangle(int x, int y, int width, int height, Color color)​

void FillRectangle(int x, int y, int width, int height, Color color);

Fill a rectangle.

DrawCircle(int cx, int cy, int radius, Color color, int thickness)​

void DrawCircle(int cx, int cy, int radius, Color color, int thickness = 1);

Midpoint-algorithm circle outline.

FillCircle(int cx, int cy, int radius, Color color)​

void FillCircle(int cx, int cy, int radius, Color color);

Filled circle.

DrawText(const std::string& text, const Font& font, int x, int y, int sizePx, Color color)​

void DrawText(const std::string& text, const Font& font,
              int x, int y, int sizePx, Color color);

Rasterize text with font at sizePx, with the top-left of the text box at (x, y). Alpha-blends against whatever is already in the canvas. Rgb565 and Monochrome targets only.

DrawImage(const Image& image, int x, int y)​

void DrawImage(const Image& image, int x, int y);

Blit a pre-decoded Image into this canvas at (x, y). Converts to the canvas's PixelFormat on the fly.

DrawImage(std::span<const uint8_t> fileBytes, int x, int y)​

void DrawImage(std::span<const uint8_t> fileBytes, int x, int y);

Decode an image file (JPEG / PNG / BMP / GIF / TGA) and blit it into this canvas at (x, y). For repeated draws, cache the decode via Image::Load instead.