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Background - I came across http://www.responsivebreakpoints.com/ the other day and thought it was a nice idea, but that could be done in PW using the API. In a nutshell, what it does is create an image width breakpoint at roughly every 20kb of file size between a minimum and maximum pixel size. According to this article on CSS-Tricks, "If you’re just changing resolutions, use srcset", so the markup is as suggested there. There is already the excellent Srcset Image Textformatter which works on images in RTE fields, but if you want responsive images elsewhere in your templates, you need to do the markup and decide on breakpoint sizes yourself. However, Field Templates have got you covered! Just save this as a field template file in /site/templates/fields/my_image.php as described above. <?php $maxWidth = 1000; //largest breakpoint $minWidth = 200; //smallest breakpoint $srcQuality = 40; //jpeg quality of the 'src' image $srcsetQuality = 80; //jpeg quality of the 'srcset' images $breakpointStepFileSize = 20; //i.e. 20kb $class = ""; //change this if you want to add eg "class='responsive'" $horizAspect = $value->width / $value->height; $minSizeArea = round($minWidth * ($minWidth / $horizAspect)); $maxSizeArea = round($maxWidth * ($maxWidth / $horizAspect)); $areaDiff = $maxSizeArea - $minSizeArea; $minFile = $value->width($minWidth, array('quality' => $srcsetQuality)); $maxFile = $value->width($maxWidth, array('quality' => $srcsetQuality)); $minFileSize = $minFile->filesize; $maxFileSize = $maxFile->filesize; $fileSizeDiff = $maxFileSize - $minFileSize; if($fileSizeDiff > ($breakpointStepFileSize * 1024)){ $numBreakpoints = round($fileSizeDiff / ($breakpointStepFileSize * 1024)); for($s = 1; $s < $numBreakpoints; $s++){ $breakpointStepArea = $minSizeArea + (($areaDiff / $numBreakpoints) * $s); $breakpointWidth = round(sqrt($breakpointStepArea * $horizAspect)); $breakpoints[] = $breakpointWidth; } } $src = $value->width($maxWidth, array('quality' => $srcQuality))->url; $min = "$minFile->url {$minWidth}w, "; $out = "<img src='$src' srcset='$min"; foreach($breakpoints as $breakpoint){ $bp = $value->width($breakpoint, array('quality' => $srcsetQuality))->url; $out .= "$bp {$breakpoint}w, "; } $out .= "$maxFile->url {$maxWidth}w"; $out .= "' alt='$value->description' $class>"; echo $out; Then use something like echo $page->render->my_image; in your page template and you'll get something like <img src='/site/assets/files/1/photo.1000x0.jpg' srcset='/site/assets/files/1/photo.200x0.jpg 200w, /site/assets/files/1/photo.482x0.jpg 482w, /site/assets/files/1/photo.651x0.jpg 651w, /site/assets/files/1/photo.785x0.jpg 785w, /site/assets/files/1/photo.899x0.jpg 899w, /site/assets/files/1/photo.1000x0.jpg 1000w' alt='pic' > (Bear in mind that PW has to create all these image variations on first page load, so it will take a moment.) Give it a try and see what you think!
