Stream output file to stdout

application/F3DStarter.cxx

@@ -15,6 +15,7 @@
 #include <algorithm>
 #include <cassert>
 #include <filesystem>
+#include <iostream>
 #include <set>
 
 namespace fs = std::filesystem;
@@ -102,28 +103,28 @@ class F3DStarter::F3DInternals
     return false;
   }
 
-  static void SetVerboseLevel(const std::string& level)
+  static void SetVerboseLevel(const std::string& level, bool forceStdErr)
   {
     // A switch/case over verbose level
     if (level == "quiet")
     {
-      f3d::log::setVerboseLevel(f3d::log::VerboseLevel::QUIET);
+      f3d::log::setVerboseLevel(f3d::log::VerboseLevel::QUIET, forceStdErr);
     }
     else if (level == "error")
     {
-      f3d::log::setVerboseLevel(f3d::log::VerboseLevel::ERROR);
+      f3d::log::setVerboseLevel(f3d::log::VerboseLevel::ERROR, forceStdErr);
     }
     else if (level == "warning")
     {
-      f3d::log::setVerboseLevel(f3d::log::VerboseLevel::WARN);
+      f3d::log::setVerboseLevel(f3d::log::VerboseLevel::WARN, forceStdErr);
     }
     else if (level == "info")
     {
-      f3d::log::setVerboseLevel(f3d::log::VerboseLevel::INFO);
+      f3d::log::setVerboseLevel(f3d::log::VerboseLevel::INFO, forceStdErr);
     }
     else if (level == "debug")
     {
-      f3d::log::setVerboseLevel(f3d::log::VerboseLevel::DEBUG);
+      f3d::log::setVerboseLevel(f3d::log::VerboseLevel::DEBUG, forceStdErr);
     }
     else
     {
@@ -164,8 +165,16 @@ int F3DStarter::Start(int argc, char** argv)
   this->Internals->Parser.GetOptions(
     this->Internals->AppOptions, this->Internals->DynamicOptions, files);
 
+  const bool renderToStdout = this->Internals->AppOptions.Output == "-";
+
   // Set verbosity level early from command line
-  F3DInternals::SetVerboseLevel(this->Internals->AppOptions.VerboseLevel);
+  F3DInternals::SetVerboseLevel(this->Internals->AppOptions.VerboseLevel, renderToStdout);
+
+  if (renderToStdout)
+  {
+    f3d::log::info("Output image will be saved to stdout, all log types including debug and info "
+                   "levels are redirected to stderr");
+  }
 
   f3d::log::debug("========== Initializing ==========");
 
@@ -184,7 +193,7 @@ int F3DStarter::Start(int argc, char** argv)
       this->Internals->AppOptions, this->Internals->DynamicOptions, files);
 
     // Set verbosity level again if it was defined in the configuration file global block
-    F3DInternals::SetVerboseLevel(this->Internals->AppOptions.VerboseLevel);
+    F3DInternals::SetVerboseLevel(this->Internals->AppOptions.VerboseLevel, renderToStdout);
   }
 
 #if __APPLE__
@@ -426,8 +435,17 @@ int F3DStarter::Start(int argc, char** argv)
       }
 
       f3d::image img = window.renderToImage(this->Internals->AppOptions.NoBackground);
-      img.save(this->Internals->AppOptions.Output);
-      f3d::log::debug("Output image saved to ", this->Internals->AppOptions.Output);
+      if (renderToStdout)
+      {
+        const auto buffer = img.saveBuffer();
+        std::copy(buffer.begin(), buffer.end(), std::ostreambuf_iterator(std::cout));
+        f3d::log::debug("Output image saved to stdout");
+      }
+      else
+      {
+        img.save(this->Internals->AppOptions.Output);
+        f3d::log::debug("Output image saved to ", this->Internals->AppOptions.Output);
+      }
 
       if (this->Internals->FilesList.size() > 1)
       {

application/testing/CMakeLists.txt

@@ -198,6 +198,8 @@ f3d_test(NAME TestUpDirectionNoSign DATA suzanne.ply ARGS --up=X DEFAULT_LIGHTS)
 f3d_test(NAME TestTextureMatCap DATA suzanne.ply ARGS --texture-matcap=${F3D_SOURCE_DIR}/testing/data/skin.png DEFAULT_LIGHTS)
 f3d_test(NAME TestTextureMatCapWithTCoords DATA WaterBottle.glb ARGS --geometry-only --texture-matcap=${F3D_SOURCE_DIR}/testing/data/skin.png DEFAULT_LIGHTS)
 f3d_test(NAME TestConfigOrder DATA suzanne.ply ARGS CONFIG ${F3D_SOURCE_DIR}/testing/data/config-order.json DEFAULT_LIGHTS)
+f3d_test(NAME TestOutputStream DATA suzanne.ply ARGS --verbose=quiet --output=- REGEXP "^.PNG" NO_BASELINE NO_OUTPUT)
+f3d_test(NAME TestOutputStreamInfo DATA suzanne.ply ARGS --verbose=info --output=- REGEXP "redirected to stderr" NO_BASELINE NO_OUTPUT)
 
 # Needs SSBO: https://gitlab.kitware.com/vtk/vtk/-/merge_requests/10675
 if(VTK_VERSION VERSION_GREATER_EQUAL 9.3.20231108)

doc/user/OPTIONS.md

@@ -6,7 +6,7 @@ F3D behavior can be fully controlled from the command line using the following o
 
 Options|Default|Description
 ------|------|------
-\-\-output=\<png file\>||Instead of showing a render view and render into it, *render directly into a png file*. When used with \-\-ref option, only outputs on failure.
+\-\-output=\<png file\>||Instead of showing a render view and render into it, *render directly into a png file*. When used with \-\-ref option, only outputs on failure. If `-` is specified instead of a filename, the PNG file is streamed to the stdout.
 \-\-no-background||Use with \-\-output to output a png file with a transparent background.
 -h, \-\-help||Print *help* and exit. Ignore `--verbose`.
 \-\-version||Show *version* information and exit. Ignore `--verbose`.

library/public/log.h

@@ -101,8 +101,10 @@ class F3D_EXPORT log
 
   /**
    * Set the verbose level.
+   * By default, only warnings and errors are written to stderr, debug and info are written to
+   * stdout. If forceStdErr is true, all messages including debug and info are written to stderr.
    */
-  static void setVerboseLevel(VerboseLevel level);
+  static void setVerboseLevel(VerboseLevel level, bool forceStdErr = false);
 
   /**
    * Wait for user if applicable (eg: win32 output window).

library/src/log.cxx

@@ -69,10 +69,20 @@ void log::setUseColoring(bool use)
 }
 
 //----------------------------------------------------------------------------
-void log::setVerboseLevel(log::VerboseLevel level)
+void log::setVerboseLevel(log::VerboseLevel level, bool forceStdErr)
 {
   detail::init::initialize();
-  F3DLog::SetQuiet(level == log::VerboseLevel::QUIET);
+
+  if (level == log::VerboseLevel::QUIET)
+  {
+    F3DLog::SetStandardStream(F3DLog::StandardStream::None);
+  }
+  else
+  {
+    F3DLog::SetStandardStream(
+      forceStdErr ? F3DLog::StandardStream::AlwaysStdErr : F3DLog::StandardStream::Default);
+  }
+
   switch (level)
   {
     case (log::VerboseLevel::DEBUG):

vtkext/private/module/F3DLog.cxx

@@ -55,10 +55,23 @@ void F3DLog::SetUseColoring(bool use)
 }
 
 //----------------------------------------------------------------------------
-void F3DLog::SetQuiet(bool quiet)
+void F3DLog::SetStandardStream(StandardStream mode)
 {
   vtkOutputWindow* win = vtkOutputWindow::GetInstance();
-  win->SetDisplayMode(quiet ? vtkOutputWindow::NEVER : vtkOutputWindow::ALWAYS);
+
+  switch (mode)
+  {
+    case StandardStream::None:
+      win->SetDisplayMode(vtkOutputWindow::NEVER);
+      break;
+    case StandardStream::AlwaysStdErr:
+      win->SetDisplayMode(vtkOutputWindow::ALWAYS_STDERR);
+      break;
+    case StandardStream::Default:
+    default:
+      win->SetDisplayMode(vtkOutputWindow::ALWAYS);
+      break;
+  }
 }
 
 //----------------------------------------------------------------------------

vtkext/private/module/F3DLog.h

@@ -23,6 +23,13 @@ enum class Severity : unsigned char
   Error
 };
 
+enum class StandardStream : unsigned char
+{
+  Default = 0,
+  None,
+  AlwaysStdErr
+};
+
 /**
  * Set this global variable to control the verbose level
  * that actually display something in Print
@@ -41,10 +48,13 @@ void Print(Severity sev, const std::string& msg);
 void SetUseColoring(bool use);
 
 /**
- * Set if any log should be shown or not.
- * Override the verbosity level completely.
+ * Determine how standard stream should be used.
+ * If mode is None, then no message is written at all (including errors).
+ * If mode is AlwaysStdErr, then all messages are written to stderr.
+ * If mode is Default, then only warnings and errors are written to stderr. Debug and info messages
+ * are written to stdout.
  */
-void SetQuiet(bool quiet);
+void SetStandardStream(StandardStream mode);
 
 /**
  * If output window is a vtkF3DWin32OutputWindow,

vtkext/private/module/Testing/TestF3DLog.cxx

@@ -27,12 +27,12 @@ int TestF3DLog(int argc, char* argv[])
   F3DLog::Print(F3DLog::Severity::Error, "Test Error\n");
 
   F3DLog::VerboseLevel = F3DLog::Severity::Info;
-  F3DLog::SetQuiet(true); // Next print calls should print nothing
+  F3DLog::SetStandardStream(F3DLog::StandardStream::None); // Next print calls should print nothing
   F3DLog::Print(F3DLog::Severity::Debug, "Test Debug Quiet ");
   F3DLog::Print(F3DLog::Severity::Info, "Test Info Quiet ");
   F3DLog::Print(F3DLog::Severity::Warning, "Test Warning Quiet ");
   F3DLog::Print(F3DLog::Severity::Error, "Test Error Quiet\n");
-  F3DLog::SetQuiet(false);
+  F3DLog::SetStandardStream(F3DLog::StandardStream::Default);
 
   // Without the object factory created, this is expected to have no effect
   F3DLog::SetUseColoring(true);