Following on the heels of last week’s post, here are a few more thoughts gleaned from the experience of attending last year’s Qt Developer Days. These are all old news, especially if you’ve been doing Qt for a while, but putting them here may be useful to you, and clears out a page of thoughts in my engineering notes!<\/p>\n
Regardless of which you choose, both classes use Qt’s copy-on-write (COW) semantics, so if you have multiple instances of the same image, you pay a small price penalty—basically the cost of the object overhead, not the memory footprint of the image itself.<\/p>\n If you have your own model already—say you’re porting an existing application, or working with a library with its own data representation—it really is a good idea to implement your own model class from Personally, my approach is that if I don’t have a data container and I’m only dealing with a handful of data items — say, up to a hundred or so objects with a half-dozen roles or so — I use Use Following on the heels of last week’s post, here are a few more thoughts gleaned from the experience of attending last year’s Qt Developer Days. These are all old news, especially if you’ve been doing Qt for a while, but putting them here may be useful to you, and clears out a page of thoughts … Continue reading More Qt tips…<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10,9],"tags":[],"class_list":["post-356","post","type-post","status-publish","format-standard","hentry","category-mobile","category-programming"],"_links":{"self":[{"href":"https:\/\/www.lothlorien.com\/kf6gpe\/wp-json\/wp\/v2\/posts\/356","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.lothlorien.com\/kf6gpe\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.lothlorien.com\/kf6gpe\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.lothlorien.com\/kf6gpe\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.lothlorien.com\/kf6gpe\/wp-json\/wp\/v2\/comments?post=356"}],"version-history":[{"count":6,"href":"https:\/\/www.lothlorien.com\/kf6gpe\/wp-json\/wp\/v2\/posts\/356\/revisions"}],"predecessor-version":[{"id":362,"href":"https:\/\/www.lothlorien.com\/kf6gpe\/wp-json\/wp\/v2\/posts\/356\/revisions\/362"}],"wp:attachment":[{"href":"https:\/\/www.lothlorien.com\/kf6gpe\/wp-json\/wp\/v2\/media?parent=356"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.lothlorien.com\/kf6gpe\/wp-json\/wp\/v2\/categories?post=356"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.lothlorien.com\/kf6gpe\/wp-json\/wp\/v2\/tags?post=356"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}QImage<\/code> vs. QPixmap<\/code><\/strong>
\nRemember that QImage<\/code> is the general-purpose class for image manipulation whose data lives in main memory, while QPixmap<\/code> objects are usually backed by the GPU. This has some ramifications for your application:<\/p>\n\n
QImage<\/code> is optimized for I\/O and direct pixel access.<\/li>\nQPixmap<\/code> is optimized for direct screen display.<\/li>\nQPixmap<\/code> objects sparingly.\n<\/ul>\nQStandardItemModel<\/code> and Performance<\/strong>
\nQt’s support for model-view-controller is great, and one of the handiest things about it is that the QStandardItemModel<\/code> class provides everything you need in a model to get going. It is, however, not necessarily the most efficient way to do so.<\/p>\nQAbstractItemModel<\/code>. I’m not bad-mouthing QStandardItemModel<\/code>, but it’s based on Qt’s collection classes, and odds are that you know better ways to store your data (especially if there’s a lot of it!) than Qt does. <\/p>\nQStandardItemModel<\/code> and don’t look back. (Qt’s collection classes are, after all, quite good for general applications). But if I’ve already got a data model, or I know I’m going to be dealing with lots and lots of objects, it’s time for a custom model that leverages my knowledge of the data set I’m wrapping.<\/p>\nQtConcurrent<\/code> for Parallel Computation<\/strong>
\nI’ve not tried this personally, but QtConcurrent<\/code> looks really cool<\/em> for doing any kind of concurrent map\/reduce style programming. If you need to write code that leverages multiple cores for concurrent computation, it’s best to look here before trying to roll your own framework using QThread<\/code>.<\/p>\n","protected":false},"excerpt":{"rendered":"