OK, I got it. Once it's all figured out, the solution seems laughably simple.

In case anybody else needs to maintain R20 compatibility and wants to use custom icon overlays, here's a solution:

In MyObject class declaration:
(R20 code)

class MyObject : public ObjectData
{
	INSTANCEOF(MyObject, ObjectData);

	// ...

private:
#if API_VERSION < 21000
	BaseBitmap *_customIcon; ///< Used to store a node's custom icon in R20
#endif
};

public:
#if API_VERSION < 21000
	MyObject() : _customIcon(nullptr)
	{
	}

	~ MyObject()
	{
		if (_customIcon)
			BaseBitmap::Free(_customIcon);
	}
#endif

In MyObject::Message():
(R20 code)

const BaseContainer &dataRef = op->GetDataInstanceRef();

//
// 1. Copy default icon into customIcon
//

// Load default icon
IconData defaultIconData;
if (!GetIcon(node->GetType(), &defaultIconData))
	return false;

// Free _customIcon if it has been allocated before, because
// it will now receive the pointer to a newly allocated BaseBitmap.
if (_customIcon)
	BaseBitmap::Free(_customIcon);

// Get the actual bitmap that is our icon
_customIcon = defaultIconData.GetClonePart();
if (!_customIcon)
	return false;

//
// 2. Blit overlay into customIcon
//

// Load overlay icon
IconData overlayIcon;
const Int32 overlayIconId = MyFunctionToGetTheIconId();
if (overlayIconId == NOTOK)
	return false;
const Bool overlayIconloaded = GetIcon(overlayIconId, &overlayIcon);
if (overlayIconloaded)
{
	BlitOverlayBitmap(overlayIcon.bmp, _customIcon, overlayIcon.x, overlayIcon.y, overlayIcon.w, overlayIcon.h, 32, 32);

	//
	// 3. Set cid->dat to use customIcon
	//
	cid->dat->bmp = _customIcon;
	cid->dat->x = 0;
	cid->dat->y = 0;
	cid->dat->w = _customIcon->GetBw();
	cid->dat->h = _customIcon->GetBh();
	cid->filled = true;
}

And BlitOverlayBitmap(), a variation of your BlitOverlayIcon():

void BlitOverlayBitmap(BaseBitmap *overlay, BaseBitmap *dest, Int32 x, Int32 y, Int32 bw, Int32 bh, Int32 xOffset, Int32 yOffset)
{
	if (!overlay || !dest)
		return;

	BaseBitmap *overlayAlpha = overlay->GetInternalChannel();
	BaseBitmap *destAlpha = dest->GetInternalChannel();

	const Int32 destW = dest->GetBw();
	const Int32 destH = dest->GetBh();
	if (bw > destW)
		bw = destW;
	if (bh + yOffset > destH)
		bh = destH - yOffset;
	if (bw + xOffset > destW)
		bw = destW - xOffset;

	UInt16 aa, a, rr, r, gg, g, bb, b;
	aa = a = rr = r = gg = g = bb = b = 0xff;

	for (Int32 py = 0; py < bh; py++)
	{
		for (Int32 px = 0; px < bw; px++)
		{
			// get color and alpha from overlay icon
			overlay->GetPixel(x + px, y + py, &r, &g, &b);
			overlay->GetAlphaPixel(overlayAlpha, x + px, y + py, &a);

			// get color and alpha from background icon if available
			dest->GetPixel(px + xOffset, py + yOffset, &rr, &gg, &bb);
			if (destAlpha)
			{
				dest->GetAlphaPixel(destAlpha, px + xOffset, py + yOffset, &aa);
			}

			// blend overlay color against existing icon background color
			Float blend = a / 255.0;
			dest->SetPixel(px + xOffset, py + yOffset, (Int32)Blend(rr, r, blend), (Int32)Blend(gg, g, blend), (Int32)Blend(bb, b, blend));

			// use only the overlay alpha if the opacity is higher to keep the original icon complete
			// and only in case the background has an alpha at all
			if (destAlpha && aa < a)
			{
				dest->SetAlphaPixel(destAlpha, px + xOffset, py + yOffset, a);
			}
		}
	}
}

Thanks for patience & support!

Cheers,
Frank

Hmm, works fine here.
macOS 10.15.6

My first try was this:
(R20 code)

BaseContainer* bc = ((BaseObject*)node)->GetDataInstance();

IconData overlayIcon;

// According to a value in the BaseContainer change the loaded overlay
const Int32 iconId = MyFunctionToGetTheIconId();
const Bool overlayIconloaded = GetIcon(iconId, &overlayIcon);
if (overlayIconloaded && iconId != NOTOK)
{
	BlitOverlayIcon(&overlayIcon, cid->dat, overlayIcon.x, overlayIcon.y, overlayIcon.w, overlayIcon.h, 16, 16);
	cid->filled = true;
}

This did draw my overlay icon, but the underlying icon is just black. It seems that cid->dat->bmp does not contain anything.

Next try:
(R20 code)

BaseContainer* bc = ((BaseObject*)node)->GetDataInstance();

// Load node's icon
if (!GetIcon(nodeType, cid->dat))
	return false;

IconData overlayIcon;

// According to a value in the BaseContainer change the loaded overlay
const Int32 iconId = MyFunctionToGetTheIconId();
const Bool overlayIconloaded = GetIcon(iconId, &overlayIcon);
if (overlayIconloaded && iconId != NOTOK)
{
	BlitOverlayIcon(&overlayIcon, cid->dat, overlayIcon.x, overlayIcon.y, overlayIcon.w, overlayIcon.h, 16, 16);
	cid->filled = true;
}

This didn't change anything. Still a black icon with my overlay on top.

Maybe GetIcon() doesn't work for some reason? Let's try AutoBitmap().

This crashes:
(R20 code)

BaseContainer* bc = ((BaseObject*)node)->GetDataInstance();

const Int32 nodeType = node->GetType();
BaseBitmap *bmp = AutoBitmap(nodeType);

bmp->CopyTo(cid->dat->bmp); // <-- crashes here!

IconData overlayIcon;

// According to a value in the BaseContainer change the loaded overlay
const Int32 iconId = MyFunctionToGetTheIconId();
const Bool overlayIconloaded = GetIcon(iconId, &overlayIcon);
if (overlayIconloaded && iconId != NOTOK)
{
	BlitOverlayIcon(&overlayIcon, cid->dat, overlayIcon.x, overlayIcon.y, overlayIcon.w, overlayIcon.h, 16, 16);
	cid->filled = true;
}

OK, so that crashes on CopyTo().

Last try, use AutoBitmap() to load the icon directly into cid->dat->bmp.
(R20 code)

BaseContainer* bc = ((BaseObject*)node)->GetDataInstance();
				
const Int32 nodeType = node->GetType();
cid->dat->bmp = AutoBitmap(nodeType);
if (!GetIcon(nodeType, cid->dat))
	return false;
				
IconData overlayIcon;
				
// According to a value in the BaseContainer change the loaded overlay
const Int32 iconId = MyFunctionToGetTheIconId();
const Bool overlayIconloaded = GetIcon(iconId, &overlayIcon);
if (overlayIconloaded && iconId != NOTOK)
{
	BlitOverlayIcon(&overlayIcon, cid->dat, overlayIcon.x, overlayIcon.y, overlayIcon.w, overlayIcon.h, 16, 16);
	cid->filled = true;
}

This does not crash, but while cid->dat has the correct x, y, b, and h values, cid->dat->bmp has size 0,0. For some reason, the normal icon shows up in the Object Manager.

How can I solve this in R20?

Thanks for any tips!!

Cheers,
Frank

Here's another question about this...

The solution offered in this thread works in R21, S22, and R23. But it does not compile in R20, because there's no customgui_iconchooser.h and no struct CustomIconSettings.

How would one do this in R20?

Thanks in advance!
Cheers,
Frank

I’m confident they will find out ;-)
Thanks for everything!

In release mode, it doesn’t crash, but after a while playing with the material, it makes my machine (not just Cinema) unresponsive and sometimes paints the Cinema UI bright green. When that happens, I get minutes of staring at the macOS beach ball, and I have to kill the Cinema process. Memory and CPU pressure is not very high though. Maybe thrashed memory?

Oh right, that really works. Hmmm, no idea what I did before to make it behave so strange.
I'll build upon this code and come back if there are any more questions.

Thanks a lot! I'll mark this solved for now.

Cheers,
Frank

Hi Manuel,

@m_magalhaes said in Crash in ChannelShader plugin:

can you reproduce the crash using only c4d shader ?

Yes, I can reproduce it with e.g. just a brick shader.

can you provide a bit of your code if not all you code (even using our sdk_support@maxon.net mailbox ?

I could, but since it's reproducible without any of my code participating, I don't think that will be necessary ;-)

Here is a screen recording:
https://frankwilleke.de/misc/screen-recording_viewport-mipmap-crash_macos.mov

I am starting Cinema in the debugger, then I create a plane and a material with a brick shader. Drag the material onto the plane... everything is still fine. Then open the Preferences and set the Texture Mode to "Mipmap".

Note that, while my plugin project is loaded in Xcode, I am not using any of the plugin in this example. It's just to have a debugger.

Cheers,
Frank

And one more piece of the puzzle: The crash only occurs if I set Preferences -> Viewport Hardware -> Texture Mode to "Mipmap". Then, it occurs even if my shader isn't even in the scene (I tried with the Brick shader). And yes, in 22.123 and also in 22.016.

Therefore, however unsettling this is, I think I can just leave my Texture Mode on "Nearest", and leave the matter up to Maxon ;-)
Since no crash report is generated, I don't have more data to provide.

My hardware is:
iMac (Retina 5K, 27-inch, 2019)
3,6 GHz 8-Core Intel Core i9
16 GB 2667 MHz DDR4
Radeon Pro 580X 8 GB

OS:
macOS 10.15.6 (19G2021)