peermaps / georender-style2png Goto Github PK

We should store raster sprite images in the style png in a section after the point, line, and area regions so that style rules can use sprites for background and foreground images.

One way this could be implemented is to store the image coordinates as the first section and those coordinates can be fed to texture2D(). This way you can perform two texture2D()s in the vertex shader for the given feature to load a sprite by its index, and then load the relevant pixel for the fragment shader based on other rules.

Here is an example that specifies 3 images:

[point section]
[line section]
[area section]
[image coordinate section:
  0, 0,  1,250,  0,32,  2, 26, // img0: minx=0,  miny=506, maxx=32, maxy=538
  0, 0,  2, 58,  0,32,  2,106, // img1: minx=0,  miny=570, maxx=32, maxy=618
  0,32,  1,250,  0,96,  2, 58, // img2: minx=32, miny=506, maxx=96, maxy=570
]
[image data section: // it should look something like this, graphically:
   ________________________
  |img0   |img2            |
  |32x32  |64x64           |
  |_______|                |
  |img1   |                |
  |32x48  |                |
  |       |________________|
  |_______|

]

This example uses integer pixel coordinates (in big endian), but we might also consider half floats (in whatever endian).

When a feature uses a sprite (or multiple sprites), it references the sprite by its index in the coordinate section plus a mode (repeat, center, ...). The modes may have additional parameters, such as an offset (x,y) or even rotations that are static or follow the contours of a geometry.

how to specify which feature labels should show up at which zoom levels?
how to specify at a zoom level, which labels should have priority (aka be bigger). (engine expects to receive labels sorted by number. whoever has higher priority will be rendered first)

more label style considerations:
labels can be styled as such:

• size
• fill and stroke color
• font (incl. bold, italic, etc.)
• spacing between the feature & the text
• repeat (how far apart the label should repeat, like for a road or river)
• follow feature (eg river)
• whether it should be rendered at x zoom levels
• priority list for where label should appear in relation to dot/sprite (eg: top, left, right, bottom). it will have a default priority list, but you should be able to specify a diff priority. also "only top and bottom, never left and right" for example.
• rotations: example: always 45 degrees, upper right in relation to point" or "going up to the right from the point" (possible if you specify "always render on right of point, then rotate." rotations happen about the point.
• padding around label (outside the box, aka margin)
• padding around label (inside the box)
• padding around point/sprite (maybe belongs in another doc?)
• box fill/box stroke (rgba)
• orientation for characters (eg: japanese characters going vertical). default is horizontal.

in some separate doc:

• how many labels you want to display, which ones, all, etc.