canvas.h

/*****************************************************************************
 * VCLib                                                                     *
 * Visual Computing Library                                                  *
 *                                                                           *
 * Copyright(C) 2021-2025                                                    *
 * Visual Computing Lab                                                      *
 * ISTI - Italian National Research Council                                  *
 *                                                                           *
 * All rights reserved.                                                      *
 *                                                                           *
 * This program is free software; you can redistribute it and/or modify      *
 * it under the terms of the Mozilla Public License Version 2.0 as published *
 * by the Mozilla Foundation; either version 2 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              *
 * Mozilla Public License Version 2.0                                        *
 * (https://www.mozilla.org/en-US/MPL/2.0/) for more details.                *
 ****************************************************************************/
 
#ifndef VCL_OPENGL2_CANVAS_H
#define VCL_OPENGL2_CANVAS_H
 
#include <vclib/io/image.h>
#include <vclib/render/concepts/render_app.h>
#include <vclib/render/read_buffer_types.h>
#include <vclib/space/core/color.h>
#include <vclib/space/core/point.h>
#include <vclib/types.h>
 
#ifdef __APPLE__
#include <OpenGL/gl.h>
#else
#ifdef _WIN32
#include <windows.h>
#endif
#include <GL/gl.h>
#endif
 
namespace vcl {
 
template<typename DerivedRenderApp>
class CanvasOpenGL2
{
protected:
    using FloatData = ReadBufferTypes::FloatData;
    using ByteData  = ReadBufferTypes::ByteData;
    using ReadData  = ReadBufferTypes::ReadData;
 
public:
    using CallbackReadBuffer = ReadBufferTypes::CallbackReadBuffer;
 
private:
    void* mWinId = nullptr;
 
    Point2<uint> mSize = {0, 0};
 
    vcl::Color mDefaultClearColor = vcl::Color::Black;
 
    CallbackReadBuffer mReadBufferCallback = nullptr;
    Point2i            mReadDepthPoint     = Point2i(-1, -1);
 
public:
    CanvasOpenGL2(
        void* winId,
        uint  width,
        uint  height,
        void* displayId = nullptr) : mWinId(winId), mSize(width, height)
    {
        static_assert(
            RenderAppConcept<DerivedRenderApp>,
            "The DerivedRenderApp must satisfy the RenderAppConcept.");
    }
 
    ~CanvasOpenGL2() {}
 
    Point2<uint> size() const { return mSize; }
 
    uint viewId() const { return 0; }
 
    void setDefaultClearColor(const Color& color)
    {
        mDefaultClearColor = color;
        glClearColor(
            mDefaultClearColor.redF(),
            mDefaultClearColor.greenF(),
            mDefaultClearColor.blueF(),
            mDefaultClearColor.alphaF());
    }
 
    void onInit()
    {
        glViewport(0, 0, mSize.x(), mSize.y());
        glClearColor(
            mDefaultClearColor.redF(),
            mDefaultClearColor.greenF(),
            mDefaultClearColor.blueF(),
            mDefaultClearColor.alphaF());
    }
 
    void onResize(uint width, uint height)
    {
        mSize = {width, height};
        glViewport(0, 0, width, height);
    }
 
    void onPaint()
    {
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
        // if depth requested, read it
        if (mReadBufferCallback) {
            DerivedRenderApp::CNV::drawContent(derived());
            readDepthData();
            glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        }
        DerivedRenderApp::CNV::draw(derived());
        DerivedRenderApp::CNV::postDraw(derived());
    }
 
    [[nodiscard]] bool onReadDepth(
        const Point2i&     point,
        CallbackReadBuffer callback = nullptr)
    {
        if (point.x() < 0 || point.y() < 0 || // point out of bounds
            point.x() >= mSize.x() || point.y() >= mSize.y()) {
            return false;
        }
 
        mReadDepthPoint     = point;
        mReadBufferCallback = callback;
        return true;
    }
 
    bool onScreenshot(
        const std::string& filename,
        uint               width  = 0,
        uint               height = 0)
    {
        (void) width;
        (void) height;
 
        std::vector<std::uint8_t> buffer(mSize.x() * mSize.y() * 4);
        // read pixels
        glReadPixels(
            0,
            0,
            GLsizei(mSize.x()),
            GLsizei(mSize.y()),
            GL_RGBA,
            GL_UNSIGNED_BYTE,
            buffer.data());
 
        // write image using stb
        bool ret = true;
        stbi_flip_vertically_on_write(1);
        try {
            saveImageData(filename, mSize.x(), mSize.y(), buffer.data());
        }
        catch (const std::exception& e) {
            ret = false;
        }
        stbi_flip_vertically_on_write(0);
 
        return ret;
    }
 
private:
    void readDepthData()
    {
        // get depth range
        std::array<GLfloat, 2> depthRange = {0, 0};
        glGetFloatv(GL_DEPTH_RANGE, depthRange.data());
 
        // get viewport heigth only
        GLint viewport[4];
        glGetIntegerv(GL_VIEWPORT, viewport);
 
        // read depth
        GLfloat depth = depthRange[1];
        glReadPixels(
            GLint(mReadDepthPoint.x()),
            GLint(viewport[3] - mReadDepthPoint.y() - 1),
            1,
            1,
            GL_DEPTH_COMPONENT,
            GL_FLOAT,
            &depth);
 
        // normalize depth into [0,1] interval
        depth = (depth - depthRange[0]) / (depthRange[1] - depthRange[0]);
 
        ReadData rd = FloatData({depth});
 
        // callback
        mReadBufferCallback(rd);
 
        // cleanup
        mReadDepthPoint     = {-1, -1};
        mReadBufferCallback = nullptr;
    }
 
    auto* derived() { return static_cast<DerivedRenderApp*>(this); }
 
    const auto* derived() const
    {
        return static_cast<const DerivedRenderApp*>(this);
    }
};
 
} // namespace vcl
 
#endif // VCL_OPENGL2_CANVAS_H