Function sh_calculate

StereoKitC/spherical_harmonics.cpp:90–143

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spherical_harmonics_t sh_calculate(void **env_map_data, tex_format_ format, int32_t face_size) {
	spherical_harmonics_t result   = {};
	size_t                col_size = tex_format_size(format);
	vec3     (*convert)(uint8_t *) = nullptr;
	switch (format) {
	case tex_format_rgba128:       convert = to_color_128;       break;
	case tex_format_rgba32:        convert = to_color_32_linear; break;
	case tex_format_rgba32_linear: convert = to_color_32;        break;
	default: return {};
	}

	float half_px = 0.5f / face_size;
	for (int32_t i = 0; i < 6; i++) {
		uint8_t *data = (uint8_t*)env_map_data[i];
		vec3 p1 = math_cubemap_corner(i * 4);
		vec3 p2 = math_cubemap_corner(i * 4+1);
		vec3 p3 = math_cubemap_corner(i * 4+2);
		vec3 p4 = math_cubemap_corner(i * 4+3); 

		for (int32_t y = 0; y < face_size; y++) {
			float py = 1 - (y / (float)face_size + half_px);

			// Top face is flipped on both axes
			if (i == 2) {
				py = 1 - py;
			}
			for (int32_t x = 0; x < face_size; x++) {
				float px = x / (float)face_size + half_px;

				// Top face is flipped on both axes
				if (i == 2) {
					px = 1 - px;
				}

				vec3 pl = vec3_lerp(p1, p4, py);
				vec3 pr = vec3_lerp(p2, p3, py);
				vec3 pt = vec3_lerp(pl, pr, px);
				pt = vec3_normalize(pt);

				vec3 color = convert(&data[(x + y * face_size) * col_size]);
				sh_add(result, pt, color);
			}
		}
	}

	float count = face_size * face_size * 6.f;
	for (int32_t i = 0; i < 9; i++)
		result.coefficients[i] /= count;

	// Apply windowing to prevent overshooting
	sh_windowing(result, .01f);

	return result;
}

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