oak-editor/app/widget/scope/histogram/histogram.cpp

/***

  Olive - Non-Linear Video Editor
  Copyright (C) 2022 Olive Team
  Modifications Copyright (C) 2025 mikesolar

  This program is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.

***/

#include "histogram.h"

#include <array>
#include <QPainter>
#include <QtMath>
#include <QVector2D>

#include "common/qtutils.h"
#include "node/node.h"

namespace olive
{

#define super ScopeBase

HistogramScope::HistogramScope(QWidget *parent)
	: super(parent)
{
}

void HistogramScope::on_init()
{
	super::on_init();

	ShaderCode secondary_code(
		FileFunctions::read_file_as_string(
			":/shaders/rgbhistogram_secondary.frag"),
		FileFunctions::read_file_as_string(":/shaders/rgbhistogram.vert"));
	pipeline_secondary_ = renderer()->create_native_shader(secondary_code);
}

void HistogramScope::on_destroy()
{
	pipeline_secondary_.clear();
	texture_row_sums_ = nullptr;

	super::on_destroy();
}

ShaderCode HistogramScope::generate_shader_code()
{
	return ShaderCode(
		FileFunctions::read_file_as_string(":/shaders/rgbhistogram.frag"),
		FileFunctions::read_file_as_string(":/shaders/default.vert"));
}

void HistogramScope::draw_scope(TexturePtr managed_tex, QVariant pipeline)
{
	float histogram_scale = 0.80f;
	// This value is eyeballed for usefulness. Until we have a geometry
	// shader approach, it is impossible to normalize against a peak
	// sum of image values.
	float histogram_base = 2.5f;
	float histogram_power = 1.0f / histogram_base;

	ShaderJob shader_job;

	shader_job.insert(QStringLiteral("viewport"),
					  NodeValue(NodeValue::k_vec2,
								QVector2D(width(), height())));
	shader_job.insert(QStringLiteral("histogram_scale"),
					  NodeValue(NodeValue::k_float, histogram_scale));
	shader_job.insert(QStringLiteral("histogram_power"),
					  NodeValue(NodeValue::k_float, histogram_power));

	if (!texture_row_sums_ || texture_row_sums_->width() != this->width() ||
		texture_row_sums_->height() != this->height()) {
		texture_row_sums_ = renderer()->create_texture(
			VideoParams(width(), height(), managed_tex->format(),
						managed_tex->channel_count()));
	}

	// Draw managed texture to a sums texture
	shader_job.insert(QStringLiteral("ove_maintex"),
					  NodeValue(NodeValue::k_texture,
								QVariant::fromValue(managed_tex)));
	renderer()->blit_to_texture(pipeline, shader_job, texture_row_sums_.get());

	// Draw sums into a histogram
	shader_job.insert(QStringLiteral("ove_maintex"),
					  NodeValue(NodeValue::k_texture,
								QVariant::fromValue(texture_row_sums_)));
	renderer()->blit(pipeline_secondary_, shader_job,
					 texture_row_sums_->params());

	// Draw line overlays
	QPainter p(paint_device());
	QFont font = p.font();
	font.setPixelSize(10);
	QFontMetrics font_metrics = QFontMetrics(font);
	QString label;
	std::vector<float> histogram_increments = { 0.00, 0.25, 0.50, 1.0 };

	int histogram_steps = histogram_increments.size();
	QVector<QLine> histogram_lines(histogram_steps + 1);
	int font_x_offset = 0;
	int font_y_offset = font_metrics.capHeight() / 2.0f;

	p.setCompositionMode(QPainter::CompositionMode_Plus);

	p.setPen(QColor(0.0, 0.6 * 255.0, 0.0));
	p.setFont(font);

	float histogram_dim_x = ceil((width() - 1.0) * histogram_scale);
	float histogram_dim_y = ceil((height() - 1.0) * histogram_scale);
	float histogram_start_dim_x = ((width() - 1.0) - histogram_dim_x) / 2.0f;
	float histogram_start_dim_y = ((height() - 1.0) - histogram_dim_y) / 2.0f;
	float histogram_end_dim_x = (width() - 1.0) - histogram_start_dim_x;

	// for (int i=0; i <= histogram_steps; i++) {
	for (std::vector<float>::iterator it = histogram_increments.begin();
		 it != histogram_increments.end(); it++) {
		histogram_lines[it - histogram_increments.begin()].setLine(
			histogram_start_dim_x,
			(histogram_dim_y * pow(1.0 - *it, histogram_base)) +
				histogram_start_dim_y,
			histogram_end_dim_x,
			(histogram_dim_y * pow(1.0 - *it, histogram_base)) +
				histogram_start_dim_y);
		label = QString::number(*it * 100, 'f', 1) + "%";
		font_x_offset = QtUtils::q_font_metrics_width(font_metrics, label) + 4;

		p.drawText(histogram_start_dim_x - font_x_offset,
				   (histogram_dim_y * pow(1.0 - *it, histogram_base)) +
					   histogram_start_dim_y + font_y_offset,
				   label);
	}
	p.drawLines(histogram_lines);
}

void HistogramScope::draw_scope_software(QPainter &p, const QImage &image)
{
	const float histogram_scale = 0.80f;
	const float histogram_base = 2.5f;

	const int histogram_dim_x = qCeil((width() - 1.0) * histogram_scale);
	const int histogram_dim_y = qCeil((height() - 1.0) * histogram_scale);
	const int histogram_start_dim_x =
		qFloor(((width() - 1.0) - histogram_dim_x) / 2.0f);
	const int histogram_start_dim_y =
		qFloor(((height() - 1.0) - histogram_dim_y) / 2.0f);
	const int histogram_end_dim_x = width() - 1 - histogram_start_dim_x;

	std::array<int, 256> r_counts{};
	std::array<int, 256> g_counts{};
	std::array<int, 256> b_counts{};

	const int src_w = image.width();
	const int src_h = image.height();

	// Limit analysis resolution to keep CPU usage reasonable.
	const int step_x = qMax(1, src_w / 512);
	const int step_y = qMax(1, src_h / 512);

	for (int sy = 0; sy < src_h; sy += step_y) {
		const uchar *src_line = image.constScanLine(sy);
		for (int sx = 0; sx < src_w; sx += step_x) {
			const uchar *src = src_line + sx * 4;
			r_counts[src[0]]++;
			g_counts[src[1]]++;
			b_counts[src[2]]++;
		}
	}

	int max_count = 1;
	for (int i = 0; i < 256; ++i) {
		max_count = qMax(max_count, r_counts[i]);
		max_count = qMax(max_count, g_counts[i]);
		max_count = qMax(max_count, b_counts[i]);
	}

	auto draw_channel = [&](const std::array<int, 256> &counts,
							const QColor &color) {
		QPen pen(color);
		pen.setWidth(2);
		p.setPen(pen);

		QVector<QPointF> points;
		points.reserve(256);
		for (int i = 0; i < 256; ++i) {
			float x =
				histogram_start_dim_x + (float(i) / 255.0f) * histogram_dim_x;
			float normalized = float(counts[i]) / float(max_count);
			float y = histogram_start_dim_y +
					  histogram_dim_y *
						  (1.0f - pow(normalized, 1.0f / histogram_base));
			points.append(QPointF(x, y));
		}
		p.drawPolyline(points.constData(), points.size());
	};

	p.setCompositionMode(QPainter::CompositionMode_Plus);
	draw_channel(r_counts, QColor(255, 0, 0));
	draw_channel(g_counts, QColor(0, 255, 0));
	draw_channel(b_counts, QColor(0, 0, 255));

	// Draw percentage line overlays
	QFont font = p.font();
	font.setPixelSize(10);
	QFontMetrics font_metrics = QFontMetrics(font);
	QString label;
	std::vector<float> histogram_increments = { 0.00, 0.25, 0.50, 1.0 };

	int histogram_steps = histogram_increments.size();
	QVector<QLine> histogram_lines(histogram_steps + 1);
	int font_x_offset = 0;
	int font_y_offset = font_metrics.capHeight() / 2.0f;

	p.setCompositionMode(QPainter::CompositionMode_SourceOver);
	p.setPen(QColor(0.0, 0.6 * 255.0, 0.0));
	p.setFont(font);

	for (std::vector<float>::iterator it = histogram_increments.begin();
		 it != histogram_increments.end(); it++) {
		histogram_lines[it - histogram_increments.begin()].setLine(
			histogram_start_dim_x,
			(histogram_dim_y * pow(1.0 - *it, histogram_base)) +
				histogram_start_dim_y,
			histogram_end_dim_x,
			(histogram_dim_y * pow(1.0 - *it, histogram_base)) +
				histogram_start_dim_y);
		label = QString::number(*it * 100, 'f', 1) + "%";
		font_x_offset = QtUtils::q_font_metrics_width(font_metrics, label) + 4;

		p.drawText(histogram_start_dim_x - font_x_offset,
				   (histogram_dim_y * pow(1.0 - *it, histogram_base)) +
					   histogram_start_dim_y + font_y_offset,
				   label);
	}
	p.drawLines(histogram_lines);
}

}