Method GetFrame

src/effects/Brightness.cpp:49–129

This method is required for all derived classes of EffectBase, and returns a modified openshot::Frame object

// This method is required for all derived classes of EffectBase, and returns a
// modified openshot::Frame object
std::shared_ptr<openshot::Frame> Brightness::GetFrame(std::shared_ptr<openshot::Frame> frame, int64_t frame_number)
{
	// Get the frame's image
	std::shared_ptr<QImage> frame_image = frame->GetImage();
	if (!frame_image)
		return frame;

	// Get keyframe values for this frame
	const float brightness_value = brightness.GetValue(frame_number);
	const float contrast_value = contrast.GetValue(frame_number);
	const float contrast_factor = (259.0f * (contrast_value + 255.0f)) / (255.0f * (259.0f - contrast_value));
	const int brightness_offset_i = static_cast<int>(255.0f * brightness_value);

	// Loop through pixels
	unsigned char *pixels = reinterpret_cast<unsigned char *>(frame_image->bits());
	const int pixel_count = frame_image->width() * frame_image->height();
	// LUT for undoing premultiplication without a per-pixel divide.
	static const std::array<float, 256> inv_alpha = [] {
		std::array<float, 256> lut{};
		lut[0] = 0.0f;
		for (int i = 1; i < 256; ++i)
			lut[i] = 255.0f / static_cast<float>(i);
		return lut;
	}();
	const auto clamp_u8 = [](int value) -> unsigned char {
		if (value < 0) return 0;
		if (value > 255) return 255;
		return static_cast<unsigned char>(value);
	};
	const auto clamp_i = [](int value) -> int {
		if (value < 0) return 0;
		if (value > 255) return 255;
		return value;
	};

	const auto adjust_contrast_and_brightness = [&](int &R, int &G, int &B) {
		R = clamp_u8(clamp_i(static_cast<int>((contrast_factor * (R - 128)) + 128.0f)) + brightness_offset_i);
		G = clamp_u8(clamp_i(static_cast<int>((contrast_factor * (G - 128)) + 128.0f)) + brightness_offset_i);
		B = clamp_u8(clamp_i(static_cast<int>((contrast_factor * (B - 128)) + 128.0f)) + brightness_offset_i);
	};

	#pragma omp parallel for if(pixel_count >= 16384) schedule(static)
	for (int pixel = 0; pixel < pixel_count; ++pixel)
	{
		const int idx = pixel * 4;

		// Split hot paths by alpha to avoid unnecessary premultiply/unpremultiply work.
		const int A = pixels[idx + 3];
		if (A <= 0)
			continue;
		int R = 0;
		int G = 0;
		int B = 0;
		if (A == 255) {
			R = pixels[idx + 0];
			G = pixels[idx + 1];
			B = pixels[idx + 2];
			adjust_contrast_and_brightness(R, G, B);