SoOffscreenRenderer(3)

📦
version 4.0.10 · 4 versions
, in fedora 43, fedora 44

SoOffscreenRenderer — okay bestie, this is the manual page for SoOffscreenRenderer from Coin, section 3 of the manual (that's the "library calls" section, iykyk). It's giving render your whole scene into a memory buffer instead of onto your screen. Sit down, hydrate, we're doing graphics. 💅✨

🌸 NAME 🌸

SoOffscreenRenderer — the class that renders scenes into offscreen buffers. No screen required, no cap. 🫶

🎀 SYNOPSIS 🎀

#include <Inventor/SoOffscreenRenderer.h>

💖 Public Types 💖

enum Components { LUMINANCE = 1, LUMINANCE_TRANSPARENCY = 2, RGB = 3,
    RGB_TRANSPARENCY = 4 }

💖 Public Member Functions 💖

  • SoOffscreenRenderer (const SbViewportRegion &viewportregion)
  • SoOffscreenRenderer (SoGLRenderAction *action)
  • ~SoOffscreenRenderer ()
  • void setComponents (const Components components)
  • Components getComponents (void) const
  • void setViewportRegion (const SbViewportRegion &region)
  • const SbViewportRegion & getViewportRegion (void) const
  • void setBackgroundColor (const SbColor &color)
  • const SbColor & getBackgroundColor (void) const
  • void setGLRenderAction (SoGLRenderAction *action)
  • SoGLRenderAction * getGLRenderAction (void) const
  • SbBool render (SoNode *scene)
  • SbBool render (SoPath *scene)
  • unsigned char * getBuffer (void) const
  • const void *const & getDC (void) const
  • SbBool writeToRGB (FILE *fp) const
  • SbBool writeToPostScript (FILE *fp) const
  • SbBool writeToPostScript (FILE *fp, const SbVec2f &printsize) const
  • SbBool writeToRGB (const char *filename) const
  • SbBool writeToPostScript (const char *filename) const
  • SbBool writeToPostScript (const char *filename, const SbVec2f &printsize) const
  • SbBool isWriteSupported (const SbName &filetypeextension) const
  • int getNumWriteFiletypes (void) const
  • void getWriteFiletypeInfo (const int idx, SbPList &extlist, SbString &fullname, SbString &description)
  • SbBool writeToFile (const SbString &filename, const SbName &filetypeextension) const
  • void setPbufferEnable (SbBool enable)
  • SbBool getPbufferEnable (void) const

💖 Static Public Member Functions 💖

  • static float getScreenPixelsPerInch (void)
  • static SbVec2s getMaximumResolution (void)

🌈 Detailed Description 🌈

The SoOffscreenRenderer class is used for rendering scenes to offscreen buffers. That's the whole vibe. 💖

So here's the tea: if you wanna render into a memory buffer instead of an on-screen OpenGL context, this class is literally your girl. And why would you even want that? Two iconic reasons:

  • generating texture maps on-the-fly, main character energy ✨
  • saving snapshots of the scene to disk files — either as pixel bitmaps, or as PostScript files for sending to a PostScript capable printer 🖨️

Here's a dead simple usage example, just the code directly related to the SoOffscreenRenderer:

SoOffscreenRenderer myRenderer(vpregion);
SoNode * root = myViewer->getSceneManager()->getSceneGraph();
SbBool ok = myRenderer.render(root);
unsigned char * imgbuffer = myRenderer.getBuffer();
// [then use image buffer in a texture, or write it to file, or whatever]

And here a complete standalone example with a moving camera saving multiple frames to disk as JPGs:

#include <Inventor/SoDB.h>
#include <Inventor/SoOffscreenRenderer.h>
#include <Inventor/engines/SoInterpolateVec3f.h>
#include <Inventor/nodes/SoCube.h>
#include <Inventor/nodes/SoDirectionalLight.h>
#include <Inventor/nodes/SoPerspectiveCamera.h>
#include <Inventor/nodes/SoSeparator.h>

#include <iostream>

int main()
{
  // Init Coin
  SoDB::init();

  // The root node
  SoSeparator * root = new SoSeparator;
  root->ref();

  // It is mandatory to have at least one light for the offscreen renderer
  SoDirectionalLight * light = new SoDirectionalLight;
  root->addChild(light);

  // It is mandatory to have at least one camera for the offscreen renderer
  SoPerspectiveCamera * camera = new SoPerspectiveCamera;
  SbRotation cameraRotation = SbRotation::identity();
  cameraRotation *= SbRotation(SbVec3f(1, 0, 0), -0.4f);
  cameraRotation *= SbRotation(SbVec3f(0, 1, 0), 0.4f);
  camera->orientation = cameraRotation;
  root->addChild(camera);

  // Something to show... A box
  SoCube * cube = new SoCube;
  root->addChild(cube);

  // Set up the two camera positions we want to move the camera between
  SoInterpolateVec3f * interpolate = new SoInterpolateVec3f;
  interpolate->input0 = SbVec3f(2, 2, 9);
  interpolate->input1 = SbVec3f(2, 2, 5);
  camera->position.connectFrom(&interpolate->output);

  // Set up the offscreen renderer
  SbViewportRegion vpRegion(400, 300);
  SoOffscreenRenderer offscreenRenderer(vpRegion);

  // How many frames to render for the video
  int frames = 5;
  std::cout << "Writing " << frames << " frames..." << std::endl;

  for (int i = 0; i < frames; i++) {
    // Update the camera position
    interpolate->alpha = float(i) / (frames - 1);

    // Render the scene
    SbBool ok = offscreenRenderer.render(root);

    // Save the image to disk
    SbString filename = SbString("coinvideo-") + (i + 1) + ".jpg";
    if (ok) {
      offscreenRenderer.writeToFile(filename.getString(), "jpg");
    } else {
      std::cout << "Error saving image: " << filename.getString() << std::endl;
      break;
    }
  }

  std::cout << "Done!" << std::endl;

  root->unref();
  return 0;
}
⚠️ Okay bestie, listen. Note that the SoOffscreenRenderer potentially allocates a fairly large amount of resources, both OpenGL and general system resources, for each instance. So you are well advised to try to reuse SoOffscreenRenderer instances, instead of constructing and destructing a new instance e.g. for each frame when generating pictures for video. Do not be out here making a fresh one every frame, that's not the move. 😭

Offscreen rendering is internally done through either a GLX offscreen context (i.e. OpenGL on X11), WGL (i.e. OpenGL on Win32), AGL (old-style OpenGL on the Mac OS X) or CGL (new-style Mac OS X). 💅

If the OpenGL driver supports the pbuffer extension, it is detected and used to provide hardware accelerated offscreen rendering. ✨

The pixel data is fetched from the OpenGL buffer with glReadPixels(), with the format and type arguments set to GL_RGBA and GL_UNSIGNED_BYTE, respectively. Which means the maximum resolution is 32 bits, 8 bits for each of the R/G/B/A components. Math! 🌸

One particular usage of the SoOffscreenRenderer is to make it render frames to be used for the construction of movies 🎬. The general technique for doing this is to iterate over the following actions:

  • move camera to correct position for frame
  • update the realTime global field (see explanation below)
  • invoke the SoOffscreenRenderer
  • dump rendered scene to file

..then you use some external tool or library to construct the movie file, for instance in MPEG format, from the set of files dumped to disk from the iterative process above.

The code would go something like the following (pseudo code style). First we need to stop the Coin library itself from doing any automatic updating of the realTime field, so your application initialization for Coin should look something like:

[...] = SoQt::init([...]); // or SoWin::init() or SoDB::init()
// ..and then immediately:

// Control realTime field ourselves, so animations within the scene
// follows "movie-time" and not "wallclock-time".
SoDB::enableRealTimeSensor(FALSE);
SoSceneManager::enableRealTimeUpdate(FALSE);
SoSFTime * realtime = SoDB::getGlobalField("realTime");
realtime->setValue(0.0);
💀 Note that it is important that the realTime field is initialized to your start-time before setting up any engines or other entities in the system that uses the realTime field. Order matters, bestie, do not skip this.

Then for the rendering loop, something like:

for (int i=0; i < NRFRAMES; i++) {
  // [...reposition camera here, if necessary...]

  // render
  offscreenrend->render(root);

  // dump to file
  SbString framefile;
  framefile.sprintf("frame%06d.rgb", i);
  offscreenrend->writeToRGB(framefile.getString());

  // advance "current time" by the frames-per-second value, which
  // is 24 fps in this example
  realtime->setValue(realtime.getValue() + 1/24.0);
}

When making movies you need to write your application control code to take care of moving the camera along the correct trajectory yourself, and to explicitly control the global realTime field. The latter is so you're able to "step" with appropriate time units for each render operation (e.g. if you want a movie that has a 24 FPS refresh rate, first render with realTime=0.0, then add 1/24s to the realTime field, render again to a new frame, add another 1/24s to the realTime field, render, and so on). 🎞️

For further information about how to control the realTime field, see documentation of SoDB::getGlobalField(), SoDB::enableRealTimeSensor(), and SoSceneManager::enableRealTimeUpdate().

If you want to use this class to create snapshots of your current viewer's view, but want to control the size of the snapshot, you need to modify the camera a bit while rendering to be sure that everything you see in the current view is visible in the snapshot. 👑

Below you'll find some pseudo code that does this. There are probably other ways to do this as well.

void render_offscreen(const SbVec2s size)
{
  SbVec2s glsize = this->getGLSize(); // size of your normal viewer
  float glar = float(glsize[0] / float(glsize[1]));
  float ar = float(size[0]) / float(size[1]);
  SoCamera * camera = this->getCamera(); // the camera you're using
  SoCamera::ViewportMapping oldmap = (SoCamera::ViewportMapping)
    camera->viewportMapping.getValue();
  float oldar = camera->aspectRatio.getValue();

  camera->viewportMapping = SoCamera::LEAVE_ALONE;
  camera->aspectRatio = ar;

  float scaleheight = 1.0f;
  if (glar > ar) {
    scaleheight = glar / ar;
    camera->scaleHeight(scaleheight);
  }
  else {
    scaleheight = ar / glar;
    camera->scaleHeight(scaleheight);
  }
  SoOffscreenRenderer * renderer = new SoOffscreenRenderer(size);
  renderer->render(root);

  // ... save image

  // restore camera
  camera->viewportMapping = oldmap;
  camera->aspectRatio = oldar;

  if (scaleheight != 1.0f) {
    camera->scaleHeight(1.0f / scaleheight);
  }
}

🦋 Member Enumeration Documentation 🦋

✨ enum SoOffscreenRenderer::Components ✨

Enumerated values for the available image formats. Pick your fighter. 🎀

See also

  • setComponents()

💜 Constructor & Destructor Documentation 💜

🌟 SoOffscreenRenderer::SoOffscreenRenderer (const SbViewportRegion & viewportregion) 🌟

Constructor. Argument is the viewportregion we should use when rendering. An internal SoGLRenderAction will be constructed for you. ✨

🌟 SoOffscreenRenderer::SoOffscreenRenderer (SoGLRenderAction * action) 🌟

Constructor. Argument is the action we should apply to the scene graph when rendering the scene. Information about the viewport is extracted from the action. 🫶

🌟 SoOffscreenRenderer::~SoOffscreenRenderer () 🌟

Destructor. It's over, bestie. 💅

💖 Member Function Documentation 💖

float SoOffscreenRenderer::getScreenPixelsPerInch (void ) [static]

okay bestie, this one is literally just giving you the screen pixels per inch resolution of your monitor. that's it. that's the whole vibe. no cap. 💅

SbVec2s SoOffscreenRenderer::getMaximumResolution (void ) [static]

Get maximum dimensions (width, height) of the offscreen buffer. heads up though: from Coin version 2 onwards, the returned value will always be (SHRT_MAX, SHRT_MAX), where SHRT_MAX on most systems is equal to 32767.

why? because the SoOffscreenRenderer can in principle generate unlimited size offscreen canvases by tiling together multiple renderings of the same scene. so yeah, it's giving limitless potential. ✨

void SoOffscreenRenderer::setComponents (const Components components)

Sets the component format of the offscreen buffer.

If set to LUMINANCE, a grayscale image is rendered. LUMINANCE_TRANSPARENCY gives us a grayscale image with transparency. RGB will give us a 24-bit image with 8 bits each for the red, green and blue component. And RGB_TRANSPARENCY yields a 32-bit image (RGB plus transparency).

The default format to render to is RGB.

warning: This will invalidate the current buffer, if any. The buffer will not contain valid data until another call to SoOffscreenRenderer::render() happens. so don't come crying to me if it's empty. 😭

SoOffscreenRenderer::Components SoOffscreenRenderer::getComponents (void ) const

Returns the component format of the offscreen buffer.

See also: setComponents()

void SoOffscreenRenderer::setViewportRegion (const SbViewportRegion & region)

Sets the viewport region.

warning: This will invalidate the current buffer, if any. The buffer will not contain valid data until another call to SoOffscreenRenderer::render() happens. periodt.

const SbViewportRegion & SoOffscreenRenderer::getViewportRegion (void ) const

Returns the viewport region. simple as that. 🦋

void SoOffscreenRenderer::setBackgroundColor (const SbColor & color)

Sets the background color. The buffer is cleared to this color before rendering. so pick something cute. 🎀

const SbColor & SoOffscreenRenderer::getBackgroundColor (void ) const

Returns the background color. iconic.

void SoOffscreenRenderer::setGLRenderAction (SoGLRenderAction * action)

Sets the render action. Use this if you have special rendering needs. special. we love a custom moment. 💅

SoGLRenderAction * SoOffscreenRenderer::getGLRenderAction (void ) const

Returns the rendering action currently used.

SbBool SoOffscreenRenderer::render (SoNode * scene)

Render the scene graph rooted at scene into our internal pixel buffer.

important note: make sure you pass in a scene node pointer which has both a camera and at least one light source below it -- otherwise you are likely to end up with just a blank or black image buffer. no cap, this happens all the time.

This mistake is easily made if you use an SoOffscreenRenderer on a scene graph from one of the standard viewer components, as you will often just leave the addition of a camera and a headlight light source to the viewer to set up. This camera and light source are then part of the viewer's private "super-graph" outside of the scope of the scene graph passed in by the application programmer. To make sure the complete scene graph (including the viewer's "private parts" (snicker)) are passed to this method, you can get the scene graph root from the viewer's internal SoSceneManager instance instead of from the viewer's own getSceneGraph() method, like this:

SoOffscreenRenderer * myRenderer = new SoOffscreenRenderer(vpregion);
SoNode * root = myViewer->getSceneManager()->getSceneGraph();
SbBool ok = myRenderer->render(root);
// [then use image buffer in a texture, or write it to file, or whatever]

If you do this and still get a blank buffer, another common problem is to have a camera which is not actually pointing at the scene geometry you want a snapshot of. If you suspect that could be the cause of problems on your end, take a look at SoCamera::pointAt() and SoCamera::viewAll() to see how you can make a camera node guaranteed to be directed at the scene geometry.

Yet another common mistake when setting up the camera is to specify values for the SoCamera::nearDistance and SoCamera::farDistance fields which doesn't not enclose the full scene. This will result in either just the background color, or that parts at the front or the back of the scene will not be visible in the rendering.

See also: writeToRGB()

SbBool SoOffscreenRenderer::render (SoPath * scene)

Render the scene path into our internal memory buffer. easy peasy.

unsigned char * SoOffscreenRenderer::getBuffer (void ) const

Returns the offscreen memory buffer. the raw pixels, bestie. 🫶

const void *const & SoOffscreenRenderer::getDC (void ) const

Win32 only: returns a direct handle to the internal DC of the offscreen context.

Useful for efficient access to the raw image under certain special circumstances. getBuffer() might be too slow, for instance due to pixel format conversion (Windows DCs are usually BGRA, while the 32-bit buffers returned from getBuffer() are RGBA).

Notes:

  • The return value is a reference to a HDC. The HDC typedef has been unwound to a native C++ type for multiplatform compatibility reasons.
  • Returned reference will contain a NULL value on other platforms.
important limitation: if the current dimensions of the SoOffscreenRenderer instance are larger than what can be rendered with a single offscreen buffer, tiling will be used by the SoOffscreenRenderer, and the returned HDC will contain only part of the full rendered image. so not the whole picture, literally. 💀

See also: getBuffer()

Since: Coin 3.1

SbBool SoOffscreenRenderer::writeToRGB (FILE * fp) const

Writes the buffer in SGI RGB format by appending it to the already open file. Returns FALSE if writing fails.

important note: do not use this method when the Coin library has been compiled as an Microsoft Windows DLL, as passing FILE* instances back or forth to DLLs is dangerous and will most likely cause a crash. This is an intrinsic limitation for Microsoft Windows DLLs. fr fr, don't do it.

SbBool SoOffscreenRenderer::writeToPostScript (FILE * fp) const

Writes the buffer in PostScript format by appending it to the already open file. Returns FALSE if writing fails.

important note: do not use this method when the Coin library has been compiled as an Microsoft Windows DLL, as passing FILE* instances back or forth to DLLs is dangerous and will most likely cause a crash. This is an intrinsic limitation for Microsoft Windows DLLs.

SbBool SoOffscreenRenderer::writeToPostScript (FILE * fp, const SbVec2f & printsize) const

Writes the buffer to a file in PostScript format, with printsize dimensions.

important note: do not use this method when the Coin library has been compiled as an Microsoft Windows DLL, as passing FILE* instances back or forth to DLLs is dangerous and will most likely cause a crash. This is an intrinsic limitation for Microsoft Windows DLLs.

SbBool SoOffscreenRenderer::writeToRGB (const char * filename) const

Opens a file with the given name and writes the offscreen buffer in SGI RGB format to the new file. If the file already exists, it will be overwritten (if permitted by the filesystem).

Returns TRUE if all went ok, otherwise FALSE.

SbBool SoOffscreenRenderer::writeToPostScript (const char * filename) const

Opens a file with the given name and writes the offscreen buffer in PostScript format to the new file. If the file already exists, it will be overwritten (if permitted by the file system).

Returns TRUE if all went OK, otherwise FALSE.

SbBool SoOffscreenRenderer::writeToPostScript (const char * filename, const SbVec2f & printsize) const

Opens a file with the given name and writes the offscreen buffer in PostScript format with printsize dimensions to the new file. If the file already exists, it will be overwritten (if permitted by the file system).

Returns TRUE if all went ok, otherwise FALSE.

SbBool SoOffscreenRenderer::isWriteSupported (const SbName & filetypeextension) const

Returns TRUE if the buffer can be saved as a file of type filetypeextension, using SoOffscreenRenderer::writeToFile(). This function needs simage v1.1 or newer.

Examples of possibly supported extensions are: "jpg", "png", "tiff", "gif", "bmp", etc. The extension match is not case sensitive.

Which formats are actually supported depends on the capabilities of Coin's support library for handling import and export of pixel data files: the simage library. If the simage library is not installed on your system, no extension output formats will be supported.

Also, note that it is possible to build and install a simage library that lacks support for most or all of the file formats it is capable of supporting. This is so because the simage library depends on other, external 3rd party libraries -- in the same manner as Coin depends on the simage library for added file format support.

The two built-in formats that are supported through the SoOffscreenRenderer::writeToRGB() and SoOffscreenRenderer::writeToPostScript() methods (for SGI RGB format and for Adobe PostScript files, respectively) are not considered by this method, as those two formats are guaranteed to always be supported through those functions.

So if you want to be guaranteed to be able to export a screenshot in your wanted format, you will have to use either one of the above mentioned method for writing SGI RGB or Adobe PostScript directly, or make sure the Coin library has been built and is running on top of a version of the simage library (that you have preferably built yourself) with the file format(s) you want support for.

This method is an extension versus the original SGI Open Inventor API.

See also: getNumWriteFiletypes(), getWriteFiletypeInfo(), writeToFile()

int SoOffscreenRenderer::getNumWriteFiletypes (void ) const

Returns the number of available exporters. Detailed information about the exporters can then be found using getWriteFiletypeInfo().

See SoOffscreenRenderer::isWriteSupported() for information about which file formats you can expect to be present.

Note that the two built-in export formats, SGI RGB and Adobe PostScript, are not counted.

This method is an extension versus the original SGI Open Inventor API.

See also: getWriteFiletypeInfo()

void SoOffscreenRenderer::getWriteFiletypeInfo (const int idx, SbPList & extlist, SbString & fullname, SbString & description)

Returns information about an image exporter. extlist is a list of filename extensions for a file format. E.g. for JPEG it is legal to use both jpg and jpeg. extlist will contain const char * pointers (you need to cast the void * pointers to const char * before using them).

fullname is the full name of the image format. description is an optional string with more information about the file format.

See SoOffscreenRenderer::isWriteSupported() for information about which file formats you can expect to be present.

This method is an extension versus the original SGI Open Inventor API.

okay bestie, here's a whole standalone, complete code example that shows you exactly which output formats are supported. copy-paste it, run it, live your truth:

#include <Inventor/SoDB.h>
#include <Inventor/SoOffscreenRenderer.h>

int
main(int argc, char **argv)
{
  SoDB::init();
  SoOffscreenRenderer * r = new SoOffscreenRenderer(*(new SbViewportRegion));
  int num = r->getNumWriteFiletypes();

  if (num == 0) {
    (void)fprintf(stdout,
                  "No image formats supported by the "
                  "SoOffscreenRenderer except SGI RGB and PostScript.\n");
  }
  else {
    for (int i=0; i < num; i++) {
      SbPList extlist;
      SbString fullname, description;
      r->getWriteFiletypeInfo(i, extlist, fullname, description);
      (void)fprintf(stdout, "%s: %s (extension%s: ",
                    fullname.getString(), description.getString(),
                    extlist.getLength() > 1 ? "s" : "");
      for (int j=0; j < extlist.getLength(); j++) {
        (void)fprintf(stdout, "%s%s", j>0 ? ", " : "", (const char*) extlist[j]);
      }
      (void)fprintf(stdout, ")\n");
    }
  }

  delete r;
  return 0;
}

See also: getNumWriteFiletypes(), writeToFile()

Since: Coin 2.3 ✨

🌸 SbBool SoOffscreenRenderer::writeToFile(const SbString & filename, const SbName & filetypeextension) const 🌸

Saves the buffer to filename, in the file type specified by filetypeextensions. 💾✨

heads up bestie!! you still have to specify the full filename for the first argument, okay? the second argument does not automatically get attached to the filename — it's literally only there to decide the file type. so don't come crying to me when your file has no extension. 😭

This method is an extension versus the original SGI Open Inventor API. (we're built different, it's giving glow-up 💅)

See also: isWriteSupported()

🦋 void SoOffscreenRenderer::setPbufferEnable(SbBool enable) 🦋

Controls whether or not SoOffscreenRenderer can use the "pbuffer" feature of OpenGL to render the scenes with hardware acceleration. 🔥

ngl, this is a dummy function in Coin — it's provided for API compatibility reasons, because honestly it's really superfluous:

Coin has internal heuristics to figure out if pbuffers are available and can be allocated and used for the SoOffscreenRenderer. The SoOffscreenRenderer will also automatically fall back on "soft" buffers if it cannot use pbuffers (or any other hardware accelerated rendering technique). no cap, it just handles it. 👑

Since: Coin 3.1

⭐ SbBool SoOffscreenRenderer::getPbufferEnable(void ) const ⭐

See SoOffscreenRenderer::setPbufferEnable(). (yes queen, same energy, that's the whole vibe) 💖

Since: Coin 3.1

👑 AUTHOR 👑

Generated automatically by Doxygen for Coin from the source code.

and that's a wrap on this whole page, bestie!! 🎀 this came from Coin, Version 4.0.10, dated Thu Jun 25 2026 00:00:00 — so if you're reading this, hi from the past, hope your offscreen renders are crisp and your buffers are never soft unless you want them to be. 🫶 periodt. 💜

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