Parker PHD28, Руководство пользователя, Страница: 120 / 157

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Crank Storyboard design guidelines
3 Crank Storyboard best practices
PHD API Reference
The PHD50 is a 5" 800x480 screen. This translates to 188 pixels per inch, so, an image
that is 48 pixels wide will take up about ¼ of an inch on the screen. The PHD28 is a 2.8"
240x320 screen. This means there are 141 pixels per inch, or in other words, an image that
is 48 pixels wide will take up less than 3/8 of an inch on the screen—however, for the
PHD28, this would represent 15 – 20% of the screen width, depending on whether it's
used in portrait or landscape orientation.
Image cropping and positioning
In order to reduce unnecessary processing, make sure to create all images with as tight a
border as possible. For example, do not create a large full-screen image composed of
transparency with a small 48x48 icon in the middle, as this will result in waste of memory
and processing power when the image is loaded, even if it's not being rotated.
In general, the dimensions of the image file should very close to the dimensions of the
visible portion of the image. For images that will need alpha-blending with other elements,
leave one row of absolutely blank pixels around its perimeter. Most image tools like GIMP
or Photoshop will do this when using the autocrop or trim feature.
For any images that will be rotated in real-time, make sure the original source image is
drawn at 0, 90, 180 or 270 degrees. Using an arbitrary angle in the original source image
will result in more empty space around the image.
To picture this, please see the two images below. This needle will be rotated during
application use, so one might assume that bringing it in at an angle doesn't matter.
However, the number of transparent pixels that have to be alpha-blended in each case is
quite different. The non-rotated image is 42x119 pixels (4,998 pixels total), but the source
image that is pre-rotated is 114x114 pixels (12,996 pixels total). Note that the images have
had a black background added to them simply to illustrate the extent of the transparent
pixels.
Image transparency
If an image does not require transparency then create it opaque, i.e. with the alpha channel
removed. When this image is loaded by Storyboard Engine, it converts it to the color depth
of the application, which allows Storyboard Engine to optimize its rendering to the
framebuffer.
Further improvements may also be made by taking icons and screen elements that do not
change and flattening them with the background color or image to create an opaque image.
Most popular images tool like GIMP or Photoshop support removing the alpha channel
from an image. To do this, load the image into the tool and choose the option to Flatten the