Compressing DDS images using QImageWriter

Question

The documentation for Qt says that QImageWriter has a setCOmpression method and that this method depends on the chosen image format. For example, for tiff images, 0 means no compression and 1 means LZW compression. By the same token, I am setting my format to dds then call this method as follows;

QImageWriter writer(dir);
writer.setFormat("dds");
writer.setCompression(5);
bool saved = writer.write(image);

image is a QImage variable of course. But there is no compression in my resulting image. I use ImageMagick to manually compress and compressed image has lower size. Qt outputs a dds file but it is not compressed. So how can I set the compression. I chose 5 as a parameter expecting that it would set compression level to DXT5.

Game_Overture · Answer 1 · 2017-05-30T20:31:15.200

A good option until Qt implements saving compressed DDS textures is to statically link SOIL2 into your project.

https://bitbucket.org/SpartanJ/soil2

You can use its save_image_as_DDS() function with a QImage like the following:

QImage *pTexture = [Your initial image]
AtlasTextureType eTextureType = [Your desired image type]

switch(eTextureType)
{
    case ATLASTEXTYPE_PNG: {
        if(false == pTexture->save("MyTexture.png")) {
            Log("failed to generate a PNG atlas", LOGTYPE_Error);
        }
    } break;

    case ATLASTEXTYPE_DTX5: {
        QImage imgProperlyFormatted = pTexture->convertToFormat(QImage::Format_RGBA8888);
        if(0 == SOIL_save_image_quality("MyTexture.dds",
                                        SOIL_SAVE_TYPE_DDS,
                                        imgProperlyFormatted.width(),
                                        imgProperlyFormatted.height(),
                                        4,
                                        imgProperlyFormatted.bits(),
                                        0))
        {
            Log("failed to generate a DTX5 atlas", LOGTYPE_Error);
        }
    } break;

    case ATLASTEXTYPE_DTX1: {
        QImage imgProperlyFormatted = pTexture->convertToFormat(QImage::Format_RGB888);
        if(0 == SOIL_save_image_quality("MyTexture.dds",
                                        SOIL_SAVE_TYPE_DDS,
                                        imgProperlyFormatted.width(),
                                        imgProperlyFormatted.height(),
                                        3,
                                        imgProperlyFormatted.bits(),
                                        0))
        {
            Log("failed to generate a DTX1 atlas", LOGTYPE_Error);
        }
    } break;
}

Kuba hasn't forgotten Monica · Answer 2 · 2017-02-17T17:27:56.873

1

There is no compression because nobody implemented it yet in the Qt version you're using. File a feature request if the feature isn't implemented in most recent Qt, patch your copy of Qt to add this feature (possibly as a backport) and please submit your change for inclusion in Qt if the most recent version doesn't implement it:)

edited Feb 17 '17 at 17:27

answered Feb 17 '17 at 16:54

Kuba hasn't forgotten Monica

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Which version is that? – dtech Feb 17 '17 at 16:56
@ddriver Whatever version the asker happens to be using :) We can't but guess here. – Kuba hasn't forgotten Monica Feb 17 '17 at 17:28
1

It just sounded like you know the particular version without it being stated or implied. And also that it is implemented in a particular version. A matter of wording I guess ;) – dtech Feb 17 '17 at 17:47

Compressing DDS images using QImageWriter

2 Answers2