Can Custom Cplusplus CHOP access TOP pixel information?

General TouchDesigner Discussion
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1

I want to process RGB data in Custom CHOP by referring to TOP like TOP to CHOP.
Can Custom CHOP access TOP pixel information?

I read the documentation, but it didn’t say anything about it.

Thank you.

2

Yes, the same code you see in the CPUMemoryTOP example can be used in CHOP to download the texture from the referenced TOP.

3

Thanks, Malcolm.

I was able to load TOP into Custom Parameter of CPlusPlus CHOP.
How do I then access the TOP RGB data?

void setupParameters(OP_ParameterManager* manager, void* reserved1) override
{
	// load TOP
	{
		OP_StringParameter sp;
		sp.name = "Inputtop";
		sp.label = "Input TOP";
		sp.page = "Input";
		OP_ParAppendResult res = manager->appendTOP(sp);
		
		if (res != OP_ParAppendResult::Success) {
			// some error handling
		}
	}
}

image

const OP_TOPInput* top = inputs->getInputTOP(0);
When I tried to get top using this as described in the CPUMemoryTOP example, I got an error that getInputTOP() can only be used with TOP.

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image2000×240 59.4 KB

(the second error was resolved)

I’m a C++ super newbie, so I may be writing it wrong.

4

Since it’s a parameter, you need to use getParTOP(), instead of of getInputTOP(). getInputTOP is only for TOPs, since they have TOPs as their input connectors

5

Thanks!

I was able to create a C Plus Plus CHOP that outputs the input TOP RGB data to each channel.
But I didn’t use getParTOP, so I have an additional question.

I wrote the following code based on the CPUMemoryTOP example.

Please tell me how to write this part using getParTOP
inputs->getTOP(inputs->getParString("Inputtop"));

void execute(CHOP_Output* output, const OP_Inputs* inputs, void* reserved1) override
	{
		const OP_TOPInput* topInput = inputs->getTOP(inputs->getParString("Inputtop"));
		if (topInput)
		{
			OP_TOPInputDownloadOptions opts;  // use default options
			OP_SmartRef<OP_TOPDownloadResult> downloadTex = topInput->downloadTexture(opts, nullptr);

			if (downloadTex)
			{
				const uint8_t* pixelData = reinterpret_cast<const uint8_t*>(downloadTex->getData());
				int width = downloadTex->textureDesc.width;
				int height = downloadTex->textureDesc.height;

				for (int y = 0; y < height; y++)
				{
					for (int x = 0; x < width; x++)
					{
						// calculate pixel data index (assume 1 pixel for every 4 bytes)
						int pixelIdx = (y * width + x) * 4;

						// set output
						output->channels[0][y * width + x] = pixelData[pixelIdx] / 255.0f;     // R
						output->channels[1][y * width + x] = pixelData[pixelIdx + 1] / 255.0f; // G
						output->channels[2][y * width + x] = pixelData[pixelIdx + 2] / 255.0f; // B
					}
				}
			}
		}
	}
6

You would create a TOP parameter using appendTOP() when creating your custom parameters. That way you can use getParTOP() on the parameter itself.