Canvas_ity: A tiny, single-header <canvas>-like 2D rasterizer for C++

Source: Hacker News

Cleaned Example (C++)

#include 
#include 

// Include the library header and implementation.
#define CANVAS_ITY_IMPLEMENTATION
#include "canvas_ity.hpp"

int main()
{
    // --------------------------------------------------------------------
    // Construct the canvas.
    // --------------------------------------------------------------------
    static const int width  = 256;
    static const int height = 256;
    canvas_ity::canvas context( width, height );

    // --------------------------------------------------------------------
    // Build a star path.
    // --------------------------------------------------------------------
    context.move_to( 128.0f,  28.0f );  context.line_to( 157.0f,  87.0f );
    context.line_to( 223.0f,  97.0f );  context.line_to( 175.0f, 143.0f );
    context.line_to( 186.0f, 208.0f );  context.line_to( 128.0f, 178.0f );
    context.line_to(  69.0f, 208.0f );  context.line_to(  80.0f, 143.0f );
    context.line_to(  32.0f,  97.0f );  context.line_to(  98.0f,  87.0f );
    context.close_path();

    // --------------------------------------------------------------------
    // Set up the drop shadow.
    // --------------------------------------------------------------------
    context.set_shadow_blur( 8.0f );
    context.shadow_offset_y = 4.0f;
    context.set_shadow_color( 0.0f, 0.0f, 0.0f, 0.5f );

    // --------------------------------------------------------------------
    // Fill the star with yellow.
    // --------------------------------------------------------------------
    context.set_color( canvas_ity::fill_style, 1.0f, 0.9f, 0.2f, 1.0f );
    context.fill();

    // --------------------------------------------------------------------
    // Draw the star with a thick red stroke and rounded points.
    // --------------------------------------------------------------------
    context.line_join = canvas_ity::rounded;
    context.set_line_width( 12.0f );
    context.set_color( canvas_ity::stroke_style, 0.9f, 0.0f, 0.5f, 1.0f );
    context.stroke();

    // --------------------------------------------------------------------
    // Draw the star again with a dashed thinner orange stroke.
    // --------------------------------------------------------------------
    float segments[] = { 21.0f, 9.0f, 1.0f, 9.0f, 7.0f, 9.0f, 1.0f, 9.0f };
    context.set_line_dash( segments, 8 );
    context.line_dash_offset = 10.0f;
    context.line_cap = canvas_ity::circle;
    context.set_line_width( 6.0f );
    context.set_color( canvas_ity::stroke_style, 0.95f, 0.65f, 0.15f, 1.0f );
    context.stroke();

    // --------------------------------------------------------------------
    // Turn off the drop shadow.
    // --------------------------------------------------------------------
    context.set_shadow_color( 0.0f, 0.0f, 0.0f, 0.0f );

    // --------------------------------------------------------------------
    // Add a shine layer over the star.
    // --------------------------------------------------------------------
    context.set_linear_gradient( canvas_ity::fill_style, 64.0f, 0.0f, 192.0f, 256.0f );
    context.add_color_stop( canvas_ity::fill_style, 0.30f, 1.0f, 1.0f, 1.0f, 0.0f );
    context.add_color_stop( canvas_ity::fill_style, 0.35f, 1.0f, 1.0f, 1.0f, 0.8f );
    context.add_color_stop( canvas_iy::fill_style, 0.45f, 1.0f, 1.0f, 1.0f, 0.8f );
    context.add_color_stop( canvas_ity::fill_style, 0.50f, 1.0f, 1.0f, 1.0f, 0.0f );

    context.global_composite_operation = canvas_ity::source_atop;
    context.fill_rectangle( 0.0f, 0.0f, 256.0f, 256.0f );

    // --------------------------------------------------------------------
    // Fetch the rendered RGBA pixels from the entire canvas.
    // --------------------------------------------------------------------
    unsigned char *image = new unsigned char[ height * width * 4 ];
    context.get_image_data( image, width, height, width * 4, 0, 0 );

    // --------------------------------------------------------------------
    // Convert to BGRA for TGA and write the file.
    // --------------------------------------------------------------------
    for ( int i = 0; i ( width & 0xFF ),
        static_cast( width >> 8 ),
        static_cast( height & 0xFF ),
        static_cast( height >> 8 ),
        32, 40
    };

    std::ofstream stream( "example.tga", std::ios::binary );
    stream.write( reinterpret_cast( header ), sizeof( header ) );
    stream.write( reinterpret_cast( image ), height * width * 4 );
    delete[] image;
}

The code above compiles and produces a example.tga image of a stylised star using the canvas_ity library.

JavaScript snippet (stand‑alone)

// Get the 2‑D drawing context.
const context = document.getElementById("example").getContext("2d");

// Build a star path.
context.moveTo(128.0, 28.0);
context.lineTo(157.0, 87.0);
context.lineTo(223.0, 97.0);
context.lineTo(175.0, 143.0);
context.lineTo(186.0, 208.0);
context.lineTo(128.0, 178.0);
context.lineTo(69.0, 208.0);
context.lineTo(80.0, 143.0);
context.lineTo(32.0, 97.0);
context.lineTo(98.0, 87.0);
context.closePath();

// Set up the drop shadow.
context.shadowBlur = 8.0;
context.shadowOffsetY = 4.0;
context.shadowColor = "rgba(0,0,0,0.5)";

// Fill the star with yellow.
context.fillStyle = "#ffe633";
context.fill();

// Draw the star with a thick red stroke and rounded points.
context.lineJoin = "round";
context.lineWidth = 12.0;
context.strokeStyle = "#e60080";
context.stroke();

// Draw the star again with a dashed thinner orange stroke.
const segments = [21.0, 9.0, 1.0, 9.0, 7.0, 9.0, 1.0, 9.0];
context.setLineDash(segments);
context.lineDashOffset = 10.0;
context.lineCap = "round";
context.lineWidth = 6.0;
context.strokeStyle = "#f2a626";
context.stroke();

// Turn off the drop shadow.
context.shadowColor = "rgba(0,0,0,0.0)";

// Add a shine layer over the star.
let gradient = context.createLinearGradient(64.0, 0.0, 192.0, 256.0);
gradient.addColorStop(0.30, "rgba(255,255,255,0.0)");
gradient.addColorStop(0.35, "rgba(255,255,255,0.8)");
gradient.addColorStop(0.45, "rgba(255,255,255,0.8)");
gradient.addColorStop(0.50, "rgba(255,255,255,0.0)");
context.fillStyle = gradient;
context.globalCompositeOperation = "source-atop";
context.fillRect(0.0, 0.0, 256.0, 256.0);

---

Complete HTML example

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Example</title>
</head>
<body>
  <canvas id="example" width="256" height="256"></canvas>

  <script>
    const context = document.getElementById("example").getContext("2d");

    // Build a star path.
    context.moveTo(128.0, 28.0);
    context.lineTo(157.0, 87.0);
    context.lineTo(223.0, 97.0);
    context.lineTo(175.0, 143.0);
    context.lineTo(186.0, 208.0);
    context.lineTo(128.0, 178.0);
    context.lineTo(69.0, 208.0);
    context.lineTo(80.0, 143.0);
    context.lineTo(32.0, 97.0);
    context.lineTo(98.0, 87.0);
    context.closePath();

    // Set up the drop shadow.
    context.shadowBlur = 8.0;
    context.shadowOffsetY = 4.0;
    context.shadowColor = "rgba(0,0,0,0.5)";

    // Fill the star with yellow.
    context.fillStyle = "#ffe633";
    context.fill();

    // Draw the star with a thick red stroke and rounded points.
    context.lineJoin = "round";
    context.lineWidth = 12.0;
    context.strokeStyle = "#e60080";
    context.stroke();

    // Draw the star again with a dashed thinner orange stroke.
    const segments = [21.0, 9.0, 1.0, 9.0, 7.0, 9.0, 1.0, 9.0];
    context.setLineDash(segments);
    context.lineDashOffset = 10.0;
    context.lineCap = "round";
    context.lineWidth = 6.0;
    context.strokeStyle = "#f2a626";
    context.stroke();

    // Turn off the drop shadow.
    context.shadowColor = "rgba(0,0,0,0.0)";

    // Add a shine layer over the star.
    let gradient = context.createLinearGradient(64.0, 0.0, 192.0, 256.0);
    gradient.addColorStop(0.30, "rgba(255,255,255,0.0)");
    gradient.addColorStop(0.35, "rgba(255,255,255,0.8)");
    gradient.addColorStop(0.45, "rgba(255,255,255,0.8)");
    gradient.addColorStop(0.50, "rgba(255,255,255,0.0)");
    context.fillStyle = gradient;
    context.globalCompositeOperation = "source-atop";
    context.fillRect(0.0, 0.0, 256.0, 256.0);
  </script>
</body>
</html>