Windows平台RTMP播放器/RTSP播放器播放窗口添加OSD文字叠加

在windows平台上，许多开发者在开发单屏多画面显示功能时，期望像监控摄像机一样，能够在播放画面中添加osd台标，以实现字符叠加效果。大多数开发者可以轻松实现这种效果。本文将以大牛直播sdk（github）在windows平台上的demo为例，简要介绍具体实现方法：

Windows平台RTMP播放器和RTSP播放器的C++ demo，以录像过程为例，动态在左上角显示一个闪动的图标以及当前时间，具体效果如下：

核心代码如下：

std::shared_ptr CSmartPlayerDlg::MakeLogo(){
    std::shared_ptr logo_image;
    if (!is_init_gdi_plus_ok_)
        return logo_image;
    if (!recoder_image_){
        static bool is_load_image_failed = false;
        if (!is_load_image_failed){
            recoder_image_.reset(Gdiplus::Image::FromFile(_T("red_circle.png")));
            if (recoder_image_ && Gdiplus::Ok != recoder_image_->GetLastStatus()){
                is_load_image_failed = true;
                recoder_image_.reset();
            }
        }
    }
    is_has_recoder_image_ = !is_has_recoder_image_;
    if (!recoder_image_){
        is_has_recoder_image_ = false;
    }
    if (m_hWnd == nullptr || !::IsWindow(m_hWnd))
        return logo_image;
    if (cur_logo_font_name_.empty()){
        cur_logo_font_name_ = FindLogoFontName();
    }
    if (cur_logo_font_name_.empty()){
        return logo_image;
    }
    Gdiplus::FontFamily font_family(cur_logo_font_name_.c_str());
    if (!font_family.IsAvailable()){
        return logo_image;
    }
    Gdiplus::Font font(&font_family, 10, Gdiplus::FontStyleBold, Gdiplus::Unit::UnitPoint);
    if (!font.IsAvailable()){
        return logo_image;
    }
    // 白色
    Gdiplus::SolidBrush solid_brush(Gdiplus::Color(255, 255, 255));
    Gdiplus::Graphics  graphics(m_hWnd);
    if (Gdiplus::Ok != graphics.GetLastStatus()){
        return logo_image;
    }
    int recoder_image_w = 18;
    int recoder_image_h = 18;
    if (recoder_image_){
        recoder_image_w = recoder_image_->GetWidth();
        recoder_image_h = recoder_image_->GetHeight();
    }
    auto image_w = recoder_image_w + 2 + 5;
    auto image_h = recoder_image_h + 5 + 5;
    graphics.SetTextRenderingHint(Gdiplus::TextRenderingHint::TextRenderingHintClearTypeGridFit);
    auto cur_time_str = MakeCurTimerStr();
    Gdiplus::RectF bounding_box(0, 0, 0, 0);
    graphics.MeasureString(cur_time_str.c_str(), -1, &font, Gdiplus::PointF(0, 0), &bounding_box);
    Gdiplus::SizeF text_size(0, 0);
    bounding_box.GetSize(&text_size);
    image_w += (int)text_size.Width;
    image_h = image_h > ((int)text_size.Height) ? image_h : ((int)text_size.Height);
    image_w += 2;
    image_h += 2;
    image_w = ByteAlign(image_w, 4);
    image_h = ByteAlign(image_h, 4);
    Gdiplus::Bitmap   bitmap(image_w, image_h, PixelFormat32bppARGB);
    if (Gdiplus::Ok != bitmap.GetLastStatus()){
        return logo_image;
    }
    Gdiplus::Graphics g(&bitmap);
    if (Gdiplus::Ok != g.GetLastStatus()){
        return logo_image;
    }
    int r_left = 2;
    int r_top = (image_h / 2) - (recoder_image_h / 2);
    r_top -= 1;
    if (is_has_recoder_image_){
        g.DrawImage(recoder_image_.get(), r_left, r_top);
    }
    r_left += recoder_image_w;
    r_left += 5;
    r_top = (image_h / 2) - (text_size.Height / 2);
    g.DrawString(cur_time_str.c_str(), -1, &font, Gdiplus::PointF(r_left, r_top), &solid_brush);
    Gdiplus::BitmapData locked_bitmapData;
    if (Gdiplus::Ok == bitmap.LockBits(nullptr, Gdiplus::ImageLockModeRead, PixelFormat32bppARGB, &locked_bitmapData)){
        auto buffer_size = locked_bitmapData.Stride * locked_bitmapData.Height;
        std::unique_ptr buffer(new NT_BYTE[buffer_size]);
        if (buffer){
            logo_image = std::make_shared(locked_bitmapData.Width, locked_bitmapData.Height);
            logo_image->stride_ = locked_bitmapData.Stride;
            memcpy(buffer.get(), locked_bitmapData.Scan0, buffer_size);
            logo_image->data_.swap(buffer);
        }
        bitmap.UnlockBits(&locked_bitmapData);
    }
    return logo_image;
}

Windows平台RTMP播放器和RTSP播放器的C# demo，增加了“设置台标”选择框，在player窗口左上角显示“叠加字符展示”，具体内容和坐标可以自定义，具体效果如下：

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核心代码如下：

//设置OSD文本
private void DrawOSD(string draw_text)
{
    // 如果是GDI渲染，文本需要自己绘制
    if (is_gdi_render_)
        return;
    if (player_handle_ == IntPtr.Zero)
        return;
    if (draw_text == null || draw_text.Length == 0)
        return;
// 在此处添加绘制OSD文本的逻辑
}
需要注意的是，如果在GDI模式下，我们可以通过数据回调到上层进行绘制，这样实现起来会更加简单：
if (btn_check_add_osd.Checked)
{
string draw_text = "叠加字符展示";
Graphics graphics = this.CreateGraphics();
SolidBrush solid_brush = new SolidBrush(Color.FromArgb(255, 255, 255));
graphics.TextRenderingHint = System.Drawing.Text.TextRenderingHint.ClearTypeGridFit;
g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.ClearTypeGridFit;
float left = playWnd.Left + 4;
float top = playWnd.Top + 4;
g.DrawString(draw_text, this.Font, solid_brush, left, top);
}
对这方面感兴趣的开发者可以自行尝试。