eink_vg

A tiny, header-only “VG_Q1” vector renderer for e-paper / embedded displays.

• Converts simple SVG files into a compact, 2-color vector bytecode format (“VG_Q1”).
• Decodes VG_Q1 byte streams and renders them onto any display class with Adafruit_GFX-like primitives.

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Public API

Include the headers:

#include "eink_vg.h"   //for drawVG_Q1
#include "vg_assets.h" //for vg_assets[] and vg_asset_t

Assets

Generated assets are emitted as:

• vg_asset_t vg_assets[] (name + pointer + length), and/or
• a static byte array named /*name*/_vg

vg_asset_t is defined as: typedef struct { const char* name; const uint8_t* data; size_t len; } vg_asset_t;

Put SVG icons in assets/svg/.

During the build, CMake runs a Python tool that generates:

<build>/.../generated/vg_assets.h

Tweaking the output size

In CMakeLists.txt the converter is called with:

• --box 64x64

To change that, call:

idf.py -DEINK_VG_BOX_W=128 -DEINK_VG_BOX_H=296 reconfigure

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Converter limitations / tips

• The bytecode renderer is 2-color (palette0/palette1). The converter maps SVG colors to index 0/1 by luma.
• Each SVG element is rendered with a single colorIndex (fill and stroke share the same index for that element).
• Keep SVGs simple (icons/logos). Text is ignored.

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drawVG_Q1()

template <class DisplayT>
bool drawVG_Q1(
    DisplayT& d,
    const uint8_t* prog,
    int16_t dx, int16_t dy, int16_t dw, int16_t dh,
    uint16_t palette0, uint16_t palette1
);

• prog: pointer to a VG_Q1 bytecode program.
• dx,dy,dw,dh: destination rectangle on your display.
• palette0 / palette1: the two colors used by the program (colorIndex 0 maps to palette0, 1 maps to palette1).
• Returns true if the program decoded successfully, false on invalid/unknown opcodes or malformed header.

Display requirements

DisplayT must provide these Adafruit_GFX-style drawing primitives:

• drawLine(x0,y0,x1,y1,color)
• drawFastHLine(x,y,w,color)
• fillRect(x,y,w,h,color) and drawRect(x,y,w,h,color)
• fillRoundRect(x,y,w,h,r,color) and drawRoundRect(x,y,w,h,r,color)
• fillCircle(x,y,r,color) and drawCircle(x,y,r,color)

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How the bytecode works

A VG_Q1 program is a stream of opcodes:

• Starts with OP_VIEWBOX followed by vbW,vbH (uint16 each)
• Followed by any number of drawing ops
• Ends with OP_END

Coordinates are int16 in “viewBox units” and are scaled into the destination rectangle using preserveAspectRatio = xMidYMid meet (uniform scale + centered).

Opcodes

Opcode	Payload	Meaning
OP_VIEWBOX	u16 vbW, u16 vbH	Declares the source coordinate system
OP_STYLE	u8 flags, u8 strokeW, u8 colorIndex	Enables fill/stroke + stroke width + palette index
OP_LINE	s16 x0,y0,x1,y1	Draw line (stroke-only behavior)
OP_RECT	s16 x,y,w,h,rx	Rect / round-rect (rx = corner radius)
OP_CIRCLE	s16 cx,cy,r	Circle
OP_POLY	u8 n, u8 pflags, n*(s16 x,y)	Polyline / polygon (POLY_CLOSED => polygon)
OP_END	–	End of stream

Style flags

• STYLE_FILL (0x01): fill shapes
• STYLE_STROKE (0x02): stroke outlines
• strokeW: thickness (1..255), implemented by drawing multiple offset lines.
• colorIndex: 0 uses palette0, 1 uses palette1.

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Notes / limitations

• OP_POLY fill uses a scanline filler with a fixed internal cap of 128 points.
• The style carries only one colorIndex for both fill and stroke (per element). Use separate SVG elements if you need multiple colors.
• This repo includes a build-time SVG→VG_Q1 converter and a working ESP-IDF example — see examples/.