Graphic3d_ArrayOfPrimitives having transparant sections

Luc Wens
Tue, 11/22/2022 - 17:39

Forums:

With Graphic3d_ArrayOfPrimitives I visualize measurement data coming from a 3D photogrammetry system.
Some sections of the data can be invisible (in the measurement data invisible parts are coded as NAN). To handle these invisible sections, I want make the vertex from the last visible point to the next visible point transparant.

The function Graphic3d_ArrayOfPrimitives::AddVertex(const gp_Pnt & theVertex,const Standard_Integer theColor32) suggest that transparancy can be set by the highest byte from theColor32, but setting the highest byte by adding 0xff << 24 does not result in transparant sections.
Am I missing something?

-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Quantity_Color theColor(1.0, 0.0, .0, Quantity_TOC_RGB);
Standard_Integer theColor32;
Standard_Integer theColor32Invisible;

Quantity_Color::Color2argb(theColor, theColor32);
theColor32Invisible = (0xff << 24) + theColor32;

if (!m_PrsLines)
{
gp_Pnt gpPoint;
const int theNbPoints = hInput3D.Rows();
m_PrsLines = Graphic3d_ArrayOfPrimitives::CreateArray(Graphic3d_TOPA_POLYLINES, theNbPoints, 0, Graphic3d_ArrayFlags_VertexColor);

bool bVisibleBefore = true, bVisible = true;
for (ChartIndex I = 0; I < theNbPoints; I++)
{
bVisible = IsVisible(I);
if (hInput3D.IsVisible(I))
{
hInput3D.GetT4x4(T4x4, I);
gpPoint.SetX(GetX(I));
gpPoint.SetY(GetY(I));
gpPoint.SetZ(GetZ(I));
}

if (bVisibleBefore && bVisible)
m_PrsLines->AddVertex(gpPoint, theColor);
if (bVisibleBefore && !bVisible)
bVisibleBefore = false;
if (!bVisibleBefore && bVisible)
{
m_PrsLines->AddVertex(gpPoint, theColor32Invisible);
bVisibleBefore = true;
}
}
}

-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

gkv311 n
Wed, 11/23/2022 - 07:45

Make sure you indicated that your arrays should be drawn with transparency Graphic3d_Aspects::SetAlphaMode(Graphic3d_AlphaMode_Blend, x) or Graphic3d_AlphaMode_MaskBlend. The result might look poor though, without enabling OIT in Graphic3d_RenderingParams

Luc Wens
Wed, 11/23/2022 - 12:41

Thank's for the pointers, if a section is invisible then it will be completely transparant, as if it is not drawn, so I would guess the OIT would not matter to much in this particular case. Correct?

I have been searching where the apply the Graphic3d_Aspects::SetAlphaMode, but can't find it. Any pointers for this?

Tnx

Luc

gkv311 n
Wed, 11/23/2022 - 13:05

If section will be completely invisible, then why putting it into array at all? Just skip it.

Luc Wens
Wed, 11/23/2022 - 14:39

Ok, fixed it by skipping invisible sections as suggested

		m_PrsLines = Graphic3d_ArrayOfPrimitives::CreateArray(Graphic3d_TOPA_SEGMENTS, theNbPoints*2, 0, Graphic3d_ArrayFlags_VertexColor);

		for (int I = 0; I < theNbPoints; I++)
		{
			if (IsVisible(I))
			{
				X = GetX(I);
				Y = GetY(I);
				Z = GetZ(I);
			}
			else
			{
				X = Y = Z = NAN;
			}

			if (!_isnan(X) && !_isnan(X_prev))
			{
				if (UseColorChannel)
					m_AISColorScale->FindColor(hMatrixColor(I), theColor);
				m_PrsLines->AddVertex(gp_Pnt(X_prev, Y_prev, Z_prev), theColor);
				m_PrsLines->AddVertex(gp_Pnt(X, Y, Z), theColor);
			}

			X_prev = X;
			Y_prev = Y;
			Z_prev = Z;		
			theColor_prev = theColor;
		}

Tnx