Glimmr Canvas-Based Drawing

version 2/101030 by Erik Temple

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  • Section: Rendered strings

    A rendered string is a graphic element that renders an indexed text string graphically. The string is read character by character from the element's "text string" property, and each character is drawn to the screen using either an image file or a bitmap. Note that rendered strings are not accessible to screen readers.

    Rendered strings need to have a font specified in their "associated font" property in order to function. A font in this sense is a special kind of object; its major task is to link letterforms (images or bitmaps), via a lookup table, with the characters they are meant to represent. Two fonts are available with Glimmr (Glimmr Image Font and Glimmr Bitmap Font), and authors are of course free to create their own fonts (see the documentation for Glimmr Drawing Commands).

    Rendered strings can be left-aligned (the default), center-aligned, or right-aligned; the alignment determines whether the origin coordinate will represent the upper left, the upper center point, or the upper right of the rendered text.

    Rendered strings can manage the display of a cursor, which is drawn as a simple vertical line whose color is determined by the "tint" property of the rendered string (see below). This functionality is not likely to be useful except when paired with something like the Glimmr Canvas Text Input Fields extension, which handles mouse and keyboard input to allow for input to be accepted and understood via a graphics window. To display a cursor, provide a number 0 or greater via a rendered string's "cursor" property. This represents the position after which the cursor will be placed; e.g. with a cursor value of 0, the cursor will appear immediately before the first character in the string. To suppress display of the cursor (the default), provide a negative number for the cursor property.

    As has been alluded to, there are two types of rendered string:

        Bitmap-rendered string - Each glyph is drawn as a bitmap; that is, with individual pixels or 'bits' drawn directly to the screen by Glimmr.

        Image-rendered string - Each glyph is drawn using a separate, external image file, preferably in PNG format.

    A bitmap-rendered string does not require any external image files, only that a valid bitmap font (such as that provided by the Glimmr Bitmap Font extension) be specified as the "associated font". As with bitmaps, we can set the "bit-size" property to set the size of each bit, and it has the same coarseness in scaling. And as with bitmaps, the "tint" and "background tint" properties define the colors of a bitmap-rendered string, with "tint" providing the color of the letterforms. When a background tint is provided, a single rectangle is drawn encompassing the entire text area of the rendered string.

    A rendered string, like a sprite, can be provided its own "scaling factor" property to adjust the size of its glyphs relative to the canvas, and it scales with an accuracy comparable to that of sprite elements. If the "background tint" property is supplied (as always, a glulx color value), a rectangle of that color will be drawn behind the rendered string. The "tint" property of an image-rendered string controls only the color of the cursor; the color of the letterforms is set in the image files.