draw simple linechart with new template-free API and libcairo

add_subdirectory(core/plot)

add_subdirectory(core/util)

add_subdirectory(core/graphics)

add_subdirectory(test/plot)

signaltk

========

signaltk is a toolkit for creating high-quality visualizations of telemetry data.

signaltk is a toolkit for creating dynamic visualizations, such as charts, diagrams

or digital signage.

Documentation: [signaltk.org](http://signaltk.org/)

# chart

add_library(signaltk-graphics STATIC

    canvas.cc)

    backend_cairo.cc)

#add_executable(test-cplot chart_test.cc)

#target_link_libraries(test-cplot cplot stx-base)

/**

 * This file is part of the "signaltk" project

 *   Copyright (c) 2018 Paul Asmuth

 *

 * libstx is free software: you can redistribute it and/or modify it under

 * the terms of the GNU General Public License v3.0. 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 <iostream>

#include "backend_cairo.h"

namespace signaltk {

CairoBackend::CairoBackend() :

  width_(1000),

  height_(600) {

  surface_ = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, width_, height_);

  ctx_ = cairo_create(surface_);

}

CairoBackend::~CairoBackend() {

  cairo_destroy(ctx_);

  cairo_surface_destroy(surface_);

}

void CairoBackend::writePNG(const char* path) {

  cairo_surface_write_to_png(surface_, path);

}

void CairoBackend::beginChart(

    int width,

    int height,

    const std::string& class_name) {}

void CairoBackend::finishChart() {}

void CairoBackend::clear(double r, double g, double b, double a) {

  cairo_set_source_rgba(ctx_, r, g, b, a);

  cairo_rectangle(ctx_, 0, 0, width_, height_);

  cairo_fill(ctx_);

}

void CairoBackend::drawRect(

    double x,

    double y,

    double width,

    double height,

    const std::string& color,

    const std::string& class_name,

    const std::string& label,

    const std::string& series) {}

void CairoBackend::drawLine(

    double x1,

    double y1,

    double x2,

    double y2,

    const std::string& class_name) {

  cairo_set_source_rgb(ctx_, 0, 0, 0);

  cairo_set_line_width(ctx_, 0.5);

  cairo_move_to(ctx_, x1, y1);

  cairo_line_to(ctx_, x2, y2);

  cairo_stroke(ctx_);

}

void CairoBackend::drawText(

    const std::string& text,

    double x,

    double y,

    const std::string& halign,

    const std::string& valign,

    const std::string& class_name,

    double rotate) {}

void CairoBackend::drawPoint(

    double x,

    double y,

    const std::string& point_type,

    double point_size,

    const std::string& color,

    const std::string& class_name /* = "" */,

    const std::string& label /* = "" */,

    const std::string& series /* = "" */) {}

void CairoBackend::drawPath(

    const std::vector<std::pair<double, double>>& points,

    const std::string& line_style,

    double line_width,

    bool smooth,

    const std::string& color,

    const std::string& class_name) {

  if (points.size() < 2) {

    return;

  }

  cairo_set_source_rgba(ctx_, 0, 0, 0, 1);

  cairo_set_line_width(ctx_, line_width);

  cairo_move_to(ctx_, points[0].first, points[0].second);

  for (size_t i = 1; i < points.size(); ++i) {

    cairo_line_to(ctx_, points[i].first, points[i].second);

  }

  cairo_stroke(ctx_);

}

void CairoBackend::beginGroup(const std::string& class_name) {}

void CairoBackend::finishGroup() {}

} // namespace signaltk

/**

 * This file is part of the "signaltk" project

 *   Copyright (c) 2018 Paul Asmuth

 *

 * libstx is free software: you can redistribute it and/or modify it under

 * the terms of the GNU General Public License v3.0. You should have received a

 * copy of the GNU General Public License along with this program. If not, see

 * <http://www.gnu.org/licenses/>.

 */

#pragma once

#include <stdlib.h>

#include <cairo.h>

#include <vector>

#include <string>

#include "rendertarget.h"

namespace signaltk {

class CairoBackend : public chart::RenderTarget {

public:

  CairoBackend();

  ~CairoBackend();

  void writePNG(const char* path);

  void beginChart(

      int width,

      int height,

      const std::string& class_name);

  void finishChart();

  void clear(double r, double g, double b, double a);

  void drawRect(

      double x,

      double y,

      double width,

      double height,

      const std::string& color,

      const std::string& class_name,

      const std::string& label,

      const std::string& series) override;

  void drawLine(

      double x1,

      double y1,

      double x2,

      double y2,

      const std::string& class_name) override;

  void drawText(

      const std::string& text,

      double x,

      double y,

      const std::string& halign,

      const std::string& valign,

      const std::string& class_name,

      double rotate = 0.0f) override;

  void drawPoint(

      double x,

      double y,

      const std::string& point_type,

      double point_size,

      const std::string& color,

      const std::string& class_name /* = "" */,

      const std::string& label /* = "" */,

      const std::string& series /* = "" */) override;

   void drawPath(

      const std::vector<std::pair<double, double>>& points,

      const std::string& line_style,

      double line_width,

      bool smooth,

      const std::string& color,

      const std::string& class_name = "") override;

  void beginGroup(const std::string& class_name) override;

  void finishGroup() override;

  uint32_t width() const {

    return width_;

  }

  uint32_t height() const {

    return height_;

  }

protected:

  uint32_t width_;

  uint32_t height_;

  cairo_surface_t* surface_;

  cairo_t* ctx_;

};

} // namespace signaltk