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OpenGL Drawing image out of multi-channel interleaved data

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Hello,

I'm hoping someone could give me a clue for implementing what I'm trying to do.

I'm reading a file containing a very large 3D array containing multichannel interleaved data (multiple GB).

Out of this big array I'm extracting only 3 arbitrary channels out of X for each frame in order to display an RGB representation.

So at the moment I have 3 arrays containing the values of each pixels in a raw for each color:

UINT16* pRedBand = new UINT16[width * height];
UINT16* pGreenBand = new UINT16[width * height];
UINT16* pBlueBand = new UINT16[width * height];

This is 2 byte unsingned data so I have been using GLushort type to try to create a bitmap buffer.

I tried to take the approach of creating a texture but every time I call glTexImage2D I get a GL_INVALID_VALUE error code most certainly due to the fact that the texture dimensions are not power of 2 for with and height.

But if I create a texture of out of power of 2 dimensions then I'll have an oversize texture and will have a wrong aspect ratio when trying to draw the texture am I right?

Have I taken a wrong approach?

How can I create an image of arbitrary size and draw it using OpenGL.

Thanks in advance!

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With what arguments are you calling glTexImage2d? Are you absolutely certain that that call is giving you the error? (put glGetError before/after the call).

Quote:


But if I create a texture of out of power of 2 dimensions then I'll have an oversize texture and will have a wrong aspect ratio when trying to draw the texture am I right?



If you do have to use PoT textures (which is kind of surprising, that hasn't been a requirement on modern hardware for a while), then there's no requirement that you draw the whole texture. When you draw you get to choose what parts of the texture you want to draw from, so the aspect ratio when you draw is entirely up to you and shouldn't be a problem. The only potential downside of PoT textures vs non-PoT is a little bit of wasted vidmem. The end result should look exactly the same.

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Hi karwosts!

Thanks for answering! The code is not rocket science and I can share it with you. The building of the image buffer is unfinished.


UINT nSamples = GetSamples();
UINT nLines = GetLines();
UINT16* pRedBand = GetRedBandBuffer();
UINT16* pGreenBand = GetGreenBandBuffer();
UINT16* pBlueBand = GetBlueBandBuffer();
GLushort* pImageBuf = new GLushort[nSamples * nLines * 3];

ZeroMemory(pImageBuf, nSamples * nLines * 3 * sizeof(GLushort));

UINT nOffset = 0;
UINT nPointer = 0;

for(UINT nHeight = 0; nHeight < nLines; nHeight++)
{
for(UINT nWidth = 0; nWidth < nSamples; nWidth++)
{
nPointer = nHeight * nWidth;
nOffset = nPointer * 3;

// Red
pImageBuf[nOffset] = pRedBand[nPointer];

// Green
pImageBuf[nOffset + 1] = pGreenBand[nPointer];

// Blue
pImageBuf[nOffset + 2] = pBlueBand[nPointer];
}
}

glEnable(GL_TEXTURE_2D);
glGenTextures(1, &m_nTexture1);
glBindTexture(GL_TEXTURE_2D, m_nTexture1);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, nSamples, nLines, 0, GL_RGB, GL_UNSIGNED_SHORT, pImageBuf);

Maybe you are better able to tell me what I am doing wrong. I went through the code and tested line by line, the gl error comes only after calling glTexImage2D.

Any thoughts?

Thanks!

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Firstly there seems to be a mistake in your loop. Shouldn't nPointer be
nPointer = nHeight * nSamples + nWidth

EDIT: Also I think that OpenGL pads rows so that they are even. So if nSamples * 3 is an odd number, glTexImage2D might be expecting rows of nSamples * 3 + 1

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