img2webgl.py

from PIL import Image
import sys

def maskify(filename):
    im = Image.open(filename)
    px = im.load()
    width, height = im.size
    stride = 32

    rows = []
    for y in range(height):
        row = []
        for x in range(0, width, stride):
            word = 0
            for i in range(stride):
                coord = (x + i, y)
                if coord[0] >= width:
                    break
                else:
                    pixel = px[coord[0], coord[1]]
                    if pixel > 0:
                        word |= (1 << i)

            row.append(word)

        rows.append(row)

    return rows

def img2webgl(rows, u, v, width, height):
    boilerplate = """
#define TOP_U {top_u}
#define TOP_V {top_v}
#define BOTTOM_U {bottom_u}
#define BOTTOM_V {bottom_v}

#define NUM_ROWS {num_rows}
#define NUM_COLS {num_cols}

const uint[NUM_ROWS * NUM_COLS] bitmap = uint[] (
{rows}
);

vec4 render_bitmap(in vec2 originalUv, in vec4 pixel) {{
    vec2 uv = vec2(originalUv.x, 1. - originalUv.y);
    if (uv.x < TOP_U || uv.x > BOTTOM_U ||
        uv.y < TOP_V || uv.y > BOTTOM_V) {{
        // Not in the u/v box.
        return pixel;
    }}

    // Pick a pixel to sample
    float x_fraction = (uv.x - TOP_U) / (BOTTOM_U - TOP_U);
    float y_fraction = (uv.y - TOP_V) / (BOTTOM_V - TOP_V);

    // Quantize to the nearest bitmap pixel
    uint x_off = uint(trunc(x_fraction * float(NUM_COLS * 32)));
    uint x_bit = x_off & 0x1fU;
    x_off >>= 5;
    uint y_off = uint(trunc(y_fraction * float(NUM_ROWS)));
    float color = float(
        (bitmap[y_off * uint(NUM_COLS) + x_off] & (1U << x_bit)) >> x_bit
    );
    return mix(pixel, vec4(color, color, color, 1.), color);
}}
""".strip()

    statements = []
    for row_idx, row in enumerate(rows):
        formatted_row = []
        for col_idx, col in enumerate(row):
            formatted_row.append('0x%08xU' % col)
        statements.append('    %s' % ', '.join(formatted_row))

    return boilerplate.format(
        top_u='%.8f' % u,
        top_v='%.8f' % v,
        bottom_u='%.8f' % (u + width),
        bottom_v='%.8f' % (v + height),
        num_rows=len(rows),
        num_cols=len(rows[0]),
        rows=",\n".join(statements)
    )

if len(sys.argv) != 6:
    raise ValueError(
        'Usage: %s <input PNG> <top left U coord> <top left V coord> ' +
        '<fraction width> <fraction height>'
    )

print(img2webgl(maskify(sys.argv[1]), float(sys.argv[2]), float(sys.argv[3]),
    float(sys.argv[4]), float(sys.argv[5])))