Frequently Asked: How can I solve a large coordinates problem during geometry display and graphics cache auto-regeneration?

Andrew Markovich
November 22, 2017

Tags: rendering getting started

Vectorization modules based on DirectX/OpenGL graphics APIs ("WinOpenGL.txv", "WinDirectX.txv" and "WinGLES2.txv") don’t render geometry accurately for large coordinates due to hardware limitations. The GPUs work with 32-bit floats and don’t know anything about 64-bit doubles that represent geometry coordinates, so double->float truncation takes place and causes geometry rendering problems (artifacts) if geometry is far from the origin.

The following example drawing shows double->float truncation artifacts. The geometry looks angular and broken, like it is attracted to a certain grid:

image1

Vectorizers can fix this rendering problem, but they require geometry cache regeneration to recompute geometry coordinates into a suitable coordinates system. For example, an application can automatically regenerate geometry cache if an image becomes inaccurate.

This method returns true if the geometry requires regeneration:

inline bool requireAutoRegen(OdGsView *pView)
{
  OdGsDevice *pDevice = pView->device();
  if (!pDevice)
    return false;
  OdRxDictionaryPtr pProps = pDevice->properties();
  if (!pProps.isNull())
  {
    if (pProps->has(OD_T("RegenCoef")))
    {
      return OdRxVariantValue(pProps->getAt(OD_T("RegenCoef")))->getDouble() > 1.;
    }
  }
  return false;
}

The RegenCoef vectorization device property represents how many pixels in the current coordinate system will be affected by the double->float conversion. An application can check whether the geometry cache is inaccurate before updating the screen and then execute cache regeneration if this is required:

if (requireAutoRegen(pView))
{
  m_pDevice->invalidate();
  if (m_pDevice->gsModel())
    m_pDevice->gsModel()->invalidate(OdGsModel::kInvalidateAll);
}

m_pDevice in this source code example represents the OdGsLayoutHelper class.

Example drawing after geometry regeneration:

image2

 

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