好多开发者在做Windows平台特别是单屏多画面显示时，希望像监控摄像机一样，可以在播放画面添加OSD台标，以实现字符叠加效果，大多开发者可很轻松的实现以上效果，针对此，本文以大牛直播SDK （Github）的Windows平台demo为例，简单介绍下具体实现：
Windows平台C++的demo，以录像过程为例，动态在左上角显示个闪动的图标+当前时间，具体效果如下：
std::shared_ptr<nt_argb_image_logo> CSmartPlayerDlg::MakeLogo()
{
std::shared_ptr<nt_argb_image_logo> 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<NT_BYTE[]> buffer(new NT_BYTE[buffer_size]);
if (buffer)
{
logo_image = std::make_shared<nt_argb_image_logo>(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C#的demo，添加了“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、坐标可自定义，具体效果如下：
//设置OSD文本
private void DrawOSD(string draw_text)
{
// gdi 绘制的话，文本请自己绘制
if (is_gdi_render_)
return;
if (player_handle_ == IntPtr.Zero)
return;
if (draw_text == null || draw_text.Length < 1)
{
NTSmartPlayerSDK.NT_SP_SetRenderARGBLogo(player_handle_, IntPtr.Zero, 0, 0, 0, 0, 0, 0, 0);
return;
}
Graphics graphics = this.CreateGraphics();
SolidBrush solid_brush = new SolidBrush(Color.FromArgb(255, 255, 255));
graphics.TextRenderingHint = System.Drawing.Text.TextRenderingHint.ClearTypeGridFit;
SizeF text_size = new SizeF();
text_size = graphics.MeasureString(draw_text, this.Font);
int image_w = (int)text_size.Width + 4;
int image_h = (int)text_size.Height + 4;
image_w = (int)ByteAlign((UInt32)image_w, 4);
image_h = (int)ByteAlign((UInt32)image_h, 4);
Bitmap bmp = new Bitmap(image_w, image_h, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
Graphics g = Graphics.FromImage(bmp);
g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.ClearTypeGridFit;
float left = image_w / 2 - text_size.Width / 2;
float top = image_h / 2 - text_size.Height / 2;
g.DrawString(draw_text, this.Font, solid_brush, left, top);
Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height);
System.Drawing.Imaging.BitmapData bmp_data = bmp.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadOnly, bmp.PixelFormat);
IntPtr ptr = bmp_data.Scan0;
int strdie = Math.Abs(bmp_data.Stride);
NTSmartPlayerSDK.NT_SP_SetRenderARGBLogo(player_handle_, ptr, strdie, bmp_data.Width,
bmp_data.Height, 6, 6, bmp_data.Width, bmp_data.Height);
// Unlock the bits.
bmp.UnlockBits(bmp_data);
}
}注意，如果GDI模式下，我们数据回调到上层绘制的，这样加起来更简单：
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);
}感兴趣的开发者可自行尝试。