Hi Nicholas,
I suspect you'd be better off using the generic interface. There is an
example in the docs that speaks to the computation of the offsets required
to achieve just such a thing.
-Piotr
On 23 June 2015 at 16:21, Nicholas Yue <yue.nicho...@gmail.com> wrote:
> Hi,
>
> I have having difficult working out the correct stride logic to write
> one scanline at a time to an OpenEXR file.
>
> The example code shows write the entire array in memory but I only have
> access to a single scanline at a time.
>
> I want to minimize the memory usage by not storing the entire image
> before writing.
>
> Here is the code.
>
> Thanks in advance.
>
> #include <stdio.h>
> #include <string>
> #include <OpenEXR/ImfOutputFile.h>
> #include <OpenEXR/ImfArray.h>
> #include <OpenEXR/ImfCompression.h>
> #include <OpenEXR/ImfChannelList.h>
> #include <OpenEXR/ImfRgba.h>
>
> // This is currently NOT working but would be a useful example to have
>
> void writeIncrementalScanline (const std::string& fileName,
> int width,
> int height)
> {
> float pixelAspectRatio = 1;
> const Imath::V2f screenWindowCenter = Imath::V2f (0, 0);
> float screenWindowWidth = 1;
> Imf::LineOrder lineOrder = Imf::INCREASING_Y;
> Imf::Compression compression = Imf::ZIPS_COMPRESSION;
> Imf::Header header(width, height,
> pixelAspectRatio,
> screenWindowCenter,
> screenWindowWidth,
> lineOrder,
> compression);
>
> header.channels().insert("rgba.R",Imf::Channel(Imf::HALF));
> header.channels().insert("rgba.G",Imf::Channel(Imf::HALF));
> header.channels().insert("rgba.B",Imf::Channel(Imf::HALF));
> header.channels().insert("rgba.A",Imf::Channel(Imf::HALF));
> Imf::OutputFile file (fileName.c_str(), header);
> Imf::FrameBuffer framebuffer;
>
> Imf::Array2D<half> redBuffer(width,1);
> Imf::Array2D<half> greenBuffer(width,1);
> Imf::Array2D<half> blueBuffer(width,1);
> Imf::Array2D<half> alphaBuffer(width,1);
> half colorChannelGreyScaleDelta = 1.0f/float(height-1);
> std::cout << "colorChannelGreyScaleDelta = " << colorChannelGreyScaleDelta
> << std::endl;
> std::cout << "height * colorChannelGreyScaleDelta = " << height *
> colorChannelGreyScaleDelta << std::endl;
>
>
> size_t xStride = sizeof(half) * 1;
> size_t yStride = width;
>
> const half *redPixels = &redBuffer[0][0];
> const half *greenPixels = &greenBuffer[0][0];
> const half *bluePixels = &blueBuffer[0][0];
> const half *alphaPixels = &alphaBuffer[0][0];
>
> framebuffer.insert("rgba.R",
> Imf::Slice(Imf::HALF,
> (char *)redPixels,
> xStride,
> yStride));
> framebuffer.insert("rgba.G",
> Imf::Slice(Imf::HALF,
> (char *)greenPixels,
> xStride,
> yStride));
> framebuffer.insert("rgba.B",
> Imf::Slice(Imf::HALF,
> (char *)bluePixels,
> xStride,
> yStride));
> framebuffer.insert("rgba.A",
> Imf::Slice(Imf::HALF,
> (char *)alphaPixels,
> xStride,
> yStride));
>
>
> for (int h=0;h<height;h++)
> {
> half grey_scale_value = colorChannelGreyScaleDelta * h;
> for (int w=0;w<width;w++)
> {
> redBuffer[w][0] = 1.;//grey_scale_value;
> greenBuffer[w][0] = 1.;//grey_scale_value;
> blueBuffer[w][0] = 1.;//grey_scale_value;
> alphaBuffer[w][0] = 1.;
> }
>
> file.setFrameBuffer(framebuffer);
> file.writePixels();
>
> }
> }
>
> int main()
> {
> const std::string fileName("IncrementalScanline.exr");
>
> const int width = 256;
> const int height = 512;
> writeIncrementalScanline (fileName, width, height);
>
> return 0;
> }
>
> Cheers
> --
> Nicholas Yue
>
>
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>
>
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