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Diffstat (limited to 'doc/develop')
| -rw-r--r-- | doc/develop/expo.rst | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/doc/develop/expo.rst b/doc/develop/expo.rst index 8f63ccbe3ef..d6fc487e030 100644 --- a/doc/develop/expo.rst +++ b/doc/develop/expo.rst @@ -107,6 +107,37 @@ refer to objects which have been created. So a menu item is just a collection of IDs of text and image objects. When adding a menu item you must create these objects first, then create the menu item, passing in the relevant IDs. +Position and alignment +~~~~~~~~~~~~~~~~~~~~~~ + +Objects are typically positioned automatically, when scene_arrange() is called. +However it is possible to position objects manually. The scene_obj_set_pos() +sets the coordinates of the top left of the object. + +All objects have a bounding box. Typically this is calculated by looking at the +object contents, in `scene_calc_arrange()`. The calculated dimensions of each +object are stored in the object's `dims` field. + +It is possible to adjust the size of an object with `scene_obj_set_size()` or +even set the bounding box, with `scene_obj_set_bbox()`. The `SCENEOF_SIZE_VALID` +flag tracks whether the width/height should be maintained when the position +changes. + +If the bounding box is larger than the object needs, the object can be aligned +to different edges within the box. Objects can be left- or right-aligned, +or centred. For text objects this applies to each line of text. Normally objects +are drawn starting at the top of their bounding box, but they can be aligned +vertically to the bottom, or centred vertically within the box. + +Where the width of a text object's bounding box is smaller than the space needed +to show the next, the text is word-wrapped onto multiple lines, assuming there +is enough vertical space. Newline characters in the next cause a new line to be +started. The measurement information is created by the Truetype console driver +and stored in an alist in `struct scene_txt_generic`. + +When the object is drawn the `ofs` field indicates the x and y offset to use, +from the top left of the bounding box. These values are affected by alignment. + Creating an expo ---------------- |