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How to set texture as shader resource?


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#1 BlurEffect   Members   -  Reputation: 159

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Posted 27 March 2014 - 01:40 AM

Hey guys,

 

In my application I want to set a texture as shader resource, so the pixel shader can sample it using the passed in uv coordinates. Generally, I know how to do it and I have it working in another place of my application. However, for one special case it just doesn't seem to work and I can't get rid of a compilation error.

I have a class Font with this function:

ID3D11ShaderResourceView* GetTexture();

And another class trying to access that function in order to get the texture and set it as a resource for the pixel shader:

pDeviceContext -> PSSetShaderResources(0, 1, m_font.GetTexture() );

(m_font is an object of the class Font, that has that GetTexture() function)

 

The compiler gives me this error:

argument of type "ID3D11ShaderResourceView *" is incompatible with parameter of type "ID3D11ShaderResourceView *const *"

 

I think I tried all combinations of constness for the return type of the GetTexture() function and nothing changed. Also, I'm building this pretty much based on a tutorial that has pretty much the same code, so I think it should be working. Especially as it is working somewhere else in my application (although I'm not getting the texture over a get-function there but pass in the address of a member texture).

 

So, please help me to solve this. Thank you very much in advance.
 



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#2 mhagain   Crossbones+   -  Reputation: 7413

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Posted 27 March 2014 - 01:59 AM

PSSetShaderResources takes a pointer to a pointer as it's parameter, whereas your GetTexture is just returning a pointer.  That's what the compiler error is telling you - this is actually nothing to do with constness, and the presence of a "const" in the error message is throwing you off; remove or ignore the "const" (for the purposes of troubleshooting this) and you'll see that it's just a straight-up old-fashioned type mismatch between "ID3D11ShaderResourceView *" and "ID3D11ShaderResourceView **" (note the second '*').

 

Your solution is:

pDeviceContext->PSSetShaderResources (0, 1, &m_font.GetTexture ()); // note the '&'

Edited by mhagain, 27 March 2014 - 02:01 AM.

It appears that the gentleman thought C++ was extremely difficult and he was overjoyed that the machine was absorbing it; he understood that good C++ is difficult but the best C++ is well-nigh unintelligible.


#3 MJP   Moderators   -  Reputation: 10205

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Posted 27 March 2014 - 11:58 AM

To elaborate a bit more, the reason it expects a pointer to a pointer is so that it can take an array of shader resource views. So that you can do something like this:

 

ID3D11ShaderResourceView* srvs[3] = { texture0, texture1, texture2 };
immContext->PSSetShaderResources(0, 3, srvs);


#4 BlurEffect   Members   -  Reputation: 159

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Posted 27 March 2014 - 01:55 PM

Thanks guys for replying, but I tried that before, I mean using

pDeviceContext -> PSSetShaderResources(0, 1, &m_font.GetTexture() );

In that case the compiler will simply tell me: '&' requires l-value

Doing the following doesn't change anything about it:

pDeviceContext -> PSSetShaderResources(0, 1, &(m_font.GetTexture()) );

When I do something like this, however, it works:

ID3D11ShaderResourceView* pTex = m_font.GetTexture();
pDeviceContext -> PSSetShaderResources(0, 1, &pTex );

What's going on? What's the problem with the getter? Any ideas?


Edited by BlurEffect, 27 March 2014 - 01:58 PM.


#5 L. Spiro   Crossbones+   -  Reputation: 12208

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Posted 27 March 2014 - 09:27 PM

That is exactly to be expected.

What do you think “&m_font.GetTexture()” is telling the compiler?

 

Maybe you hope it returns an address to the temporary where the result of m_font.GetTexture() might be stored, but who said it would ever be stored as a temporary?

Functions return results in the EAX register on x86 machines (as a specific example), so does &m_font.GetTexture() mean “address of a register”?

Does it mean “address of the GetTexture() method itself”?

 

In your 3rd case you are explicitly creating a temporary and then passing the address of that temporary.  This is what you thought the first 2 cases would do, but the compiler is not required to make a temporary at all and it won’t allow you to rely on such behavior.

 

 

L. Spiro


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