Reading from a floating point texture resource

Graphics and GPU Programming Programming

Started by Matt_Aufderheide January 26, 2017 04:07 AM

5 comments, last by Nik02 7 years, 2 months ago

Matt_Aufderheide

361

Author

January 26, 2017 04:07 AM

HI, im trying to read data from a mapped resource that is in FLOAT_32 format

the texture is 4096*4096.. I'm trying to read into a 2D array of floats like this : heightmap_array[4096][4096]....

it seems to work ok, but I suspect something is wrong..because it seems to be too low res or something: (but the file doesn't have mipmaps) the problem might be in this line:

int rowStart = mappedResource.RowPitch*(row / sizeof(float));

not sure if this is really right.. meaning the sizeof(float) part.. is that needed? however without it, it seems to not get enough data to fill the array

void load_heightmap()
{
int heightmapsize = 4096;

D3D11_MAPPED_SUBRESOURCE mappedResource;
d3d11DevCon->Map(heightmap_res, NULL, D3D11_MAP_READ, NULL, &mappedResource);

float *sptr =(float*)(mappedResource.pData);
if (!sptr)
{
d3d11DevCon->Unmap(heightmap_res, 0);
heightmap_res->Release();
MessageBox(NULL, L"Error mapping heightmap data",
L"Error", MB_OK | MB_ICONERROR);
return;
}

// Loop through all pixels in texture and copy to output buffer
for (int row = 0; row < heightmapsize; row++)
{
int rowStart = mappedResource.RowPitch*(row / sizeof(float));
for (int col = 0; col < heightmapsize; col++)
{
heightmap_array[col][row] = sptr[(rowStart + col)];
}
}

d3d11DevCon->Unmap(heightmap_res, 0);
heightmap_res->Release();
}

Matt_Aufderheide

361

Author

January 26, 2017 04:18 AM

OK, it figures I solve the issue immediately after i post my question....however, I still dont know why its happening...

I found that changing this line:

int rowStart = mappedResource.RowPitch*(row/sizeof(float)); to

int rowStart = mappedResource.RowPitch*(row*0.25);

solves the problem, now all seems to be right...anyone understand whats going on here? Is there anything I need to be aware of?

MJP

20,295

January 26, 2017 08:37 AM

So you're reading from the mapped data using a pointer of type "float", but "RowPitch" is in bytes. You can make this a bit easier by working with a byte pointer instead of a float pointer, so that you can perform your arithmetic in terms of bytes instead of 4-byte floats. Try something like this

uint8_t* sptr = (uint8_t*)(mappedResource.pData);

for(int row = 0; row < heightmapsize; row++)
{
    float* rowStart = (float*)(sptr + (mappedResource.RowPitch * row))
    for (int col = 0; col < heightmapsize; col++)
    {
        heightmap_array[col][row] = rowStart[col];
    }
}

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Nik02

4,359

January 26, 2017 11:07 AM

row/sizeof(float) is an integer division :)

Niko Suni

Anthony Serrano

3,309

January 26, 2017 10:02 PM

row/sizeof(float) is an integer division :)

This is the real answer right here. That is an integer divide, and putting it in parentheses causes it to be evaluated in full before evaluating the rest of the expression.

To get it to work as intended you need to remove the parentheses, turning


int rowStart = mappedResource.RowPitch*(row/sizeof(float));

into


int rowStart = mappedResource.RowPitch*row/sizeof(float);

Matt_Aufderheide

361

Author

January 26, 2017 11:15 PM

Ok guys, I think i understand better now.. its working fine now. Thanks

Nik02

4,359

January 27, 2017 09:00 AM

The code that MJP posted is more efficient, though, as it does not use any divisions and only integer math :)

Niko Suni

Reading from a floating point texture resource

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