wxWidgets第十七课 采用AGG渲染库

wxWidgets可以使用不同的渲染库来呈现视图，其中AGG渲染库是一种高质量的图形渲染库，可以满足高质量的渲染和图形需求。本文将介绍如何在wxWidgets中采用AGG渲染库进行渲染。

1、安装AGG渲染库

AGG渲染库可以从官网（http://www.antigrain.com）下载。下载解压缩之后，将agg/include/agg_config.h.in文件改名为agg/include/agg_config.h，并将其拷贝到/usr/include目录下。

2、在wxWidgets中采用AGG渲染库

为了在wxWidgets中使用AGG渲染库，我们需要编写一个AGG渲染器，为wxWidgets中的DC类提供AGG渲染的实现。以下是一个简单的AGG渲染器的示例代码：

#include "wx/dc.h"
#include "agg_renderer.h"
#include "agg_trans_affine.h"
#include "agg_color_rgba.h"
#include "agg_basics.h"
#include "agg_path_storage.h"
#include "agg_conv_stroke.h"

class AggRenderer : public wxDC {
public:
    AggRenderer(wxWindow* window) : wxDC() {
        m_window = window;
        m_renderBuffer = nullptr;
        m_renderWidth = -1;
        m_renderHeight = -1;
    }

    ~AggRenderer() {
        if (m_renderBuffer != nullptr) {
            delete m_renderBuffer;
            m_renderBuffer = nullptr;
        }
    }

    void SetUserScale(double x, double y) override {
        wxDC::SetUserScale(x, y);
        m_transform = agg::trans_affine(m_scaleX, 0, 0, m_scaleY, 0, 0);
    }

    void SetDeviceOrigin(int x, int y) override {
        wxDC::SetDeviceOrigin(x, y);
        m_transform *= agg::trans_affine_translation(x, y);
    }

    void SetLogicalFunction(wxRasterOperationMode function) override {
        wxDC::SetLogicalFunction(function);

        agg::pixfmt_rgba32 pixfmt((unsigned char*)m_renderBuffer, m_renderWidth, m_renderHeight, m_renderWidth * 4);
        m_rendererBase.reset(new agg::renderer_base<pixfmt>);
    }

    void BeginDrawing() override {
        if (m_renderBuffer == nullptr || m_renderWidth != m_window->GetClientSize().GetWidth() || m_renderHeight != m_window->GetClientSize().GetHeight()) {
            m_renderWidth = m_window->GetClientSize().GetWidth();
            m_renderHeight = m_window->GetClientSize().GetHeight();
            if (m_renderBuffer != nullptr) {
                delete m_renderBuffer;
                m_renderBuffer = nullptr;
            }

            m_renderBuffer = new unsigned char[m_renderWidth * m_renderHeight * 4];
        }
    }

    void EndDrawing() override {
        wxBitmap bitmap(wxImage(m_renderWidth, m_renderHeight, m_renderBuffer, true));
        wxClientDC dc(m_window);
        dc.DrawBitmap(bitmap, 0, 0);
    }

    void Clear() override {
        agg::rect_i r(0, 0, m_renderWidth, m_renderHeight);
        m_rendererBase->clear(agg::rgba(255, 255, 255));
    }

    void SetPen(const wxPen& pen) override {
        agg::path_storage path;
        path.move_to(0.0, 0.0);
        path.line_to((double)m_deviceOriginX, (double)m_deviceOriginY);

        agg::conv_stroke<agg::path_storage> strokePath(path);
        strokePath.width(pen.GetWidth());
        strokePath.line_cap(agg::butt_cap);
        strokePath.line_join(agg::miter_join);
        strokePath.miter_limit(10.0);

        m_rendererPath.reset(new agg::renderer_scanline_aa<agg::renderer_base<agg::pixfmt_rgba32>>(*m_rendererBase));
        m_rendererPath->color(agg::rgba8(pen.GetColour().Red(), pen.GetColour().Green(), pen.GetColour().Blue(), pen.GetColour().Alpha()));
        agg::render_scanlines(strokePath, *m_rendererPath);
    }

private:
    wxWindow* m_window;
    unsigned char* m_renderBuffer;
    int m_renderWidth;
    int m_renderHeight;
    agg::trans_affine m_transform;
    std::unique_ptr<agg::renderer_base<agg::pixfmt_rgba32>> m_rendererBase;
    std::unique_ptr<agg::renderer_scanline_aa<agg::renderer_base<agg::pixfmt_rgba32>>> m_rendererPath;
};

这个AGG渲染器支持用户缩放和设备原点设置，并提供了清除函数和笔设置函数。

3、使用AGG渲染器

可以通过下面这个代码段来使用AGG渲染器：

#include "agg_renderer.h"
#include "wx/wx.h"

class MyApp : public wxApp {
public:
    bool OnInit() override {
        wxFrame* frame = new wxFrame(nullptr, wxID_ANY, "AGG Renderer Example");
        frame->SetSize(640, 480);
        frame->Show();
        SetTopWindow(frame);

        AggRenderer renderer(frame);
        renderer.BeginDrawing();
        renderer.Clear();

        renderer.SetPen(wxPen(wxColour(255, 0, 0, 255), 5));
        renderer.SetUserScale(1.0, -1.0);
        renderer.SetDeviceOrigin(0, renderer.GetSize().y);

        agg::path_storage path;
        path.move_to(0.0, 0.0);
        path.line_to(100.0, 100.0);
        path.line_to(200.0, 0.0);
        path.line_to(300.0, 100.0);

        agg::conv_stroke<agg::path_storage> strokePath(path);
        strokePath.width(1.0);
        strokePath.line_cap(agg::butt_cap);
        strokePath.line_join(agg::miter_join);
        strokePath.miter_limit(10.0);

        renderer.SetPen(wxPen(wxColour(255, 0, 0, 255), 5));
        agg::renderer_scanline_aa<agg::renderer_base<agg::pixfmt_rgba32>> rendererPath(agg::renderer_base<agg::pixfmt_rgba32>((unsigned char*)renderer.GetBuffer(), renderer.GetSize().x, renderer.GetSize().y, renderer.GetSize().x * 4));
        rendererPath.color(agg::rgba8(255, 0, 0, 255));
        agg::render_scanlines(strokePath, rendererPath);

        renderer.EndDrawing();

        return true;
    }
};

IMPLEMENT_APP(MyApp);

这个示例程序使用AGG渲染器渲染四段线段，颜色为红色。

总结

使用AGG渲染库可以实现高质量的图形渲染和绘制，对于需要高质量渲染和图形的应用程序非常有用。在wxWidgets中使用AGG渲染器可以方便地实现高质量的渲染和绘制。