NML:Alternative sprites

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Block Syntax

alternative_sprites

A alternative_sprites block allows you to specify alternative sprites (zoom levels and / or 32bpp) that are drop-in replacements for some real sprites in your grf. The syntax is as follows:

alternative_sprites(block_name, zoom_level, type[, filename[, mask_filename]]) {
	list of realsprites
}

block_name

block_name is the name of the replace / base_graphics, replace_new, font_glyph or spriteset-block for which you want to provide alternative sprites. zoom_level can be

zoom_level

name zoom level Grid size Groundsprite with zig-zag border Groundsprite with smooth border offset_x, offset_y with smooth border Description
ZOOM_LEVEL_OUT_8X 8x out 8 x 4 8 x 3 8 x 3 -3, 0 zoomed-out
ZOOM_LEVEL_OUT_4X 4x out 16 x 8 16 x 7 16 x 7 -7, 0
ZOOM_LEVEL_OUT_2X 2x out 32 x 16 32 x 15 32 x 15 -15, 0
ZOOM_LEVEL_NORMAL (normal) 64 x 32 64 x 31 64 x 31 -31, 0 The standard
ZOOM_LEVEL_IN_2X 2x in 128 x 64 128 x 62 128 x 63 -62, -1 zoomed-in
ZOOM_LEVEL_IN_4X 4x in 256 x 128 256 x 124 256 x 127 -124, -2
(X)x in (X*32) x (X*16) (X*32) x floor(X*15) (X*32) x (X*16-1) ceil(X*-31), ceil(X*-1/2) Generalisation

Hint: If you have a normal-zoom sprite with (offset_x, yel), the 2x zoom-in sprite will have (2*offset_x, 2*offset_y-1), and the 4x zoom-in sprite will have (4*offset_x, 4*offset_y-2).

These conversions are implied by how OpenTTD draws foundations, in particular half-tile foundations. At 1x zoom the vertical slope edge is between two pixels, and the horizontal slope edge is in the middle of a pixel. That is: The middle of the tiles (green line) needs to line up, the top of the tiles (red line) then does not line up: Groundsprites 4x.png

type

The type argument specifies which kind of sprite follows. This may be either BIT_DEPTH_8BPP or BIT_DEPTH_32BPP.

filename

Specifying a filename is optional, it's only useful if you have multiple sprites in the same file. If every sprite is in a separate file you'll have to specify the filename for each realsprite anyway, so you can leave it out of the alternative_sprites-block.

mask_filename

For 32bpp only, you can also specify a default filename to use for mask sprites. These (8bpp) sprites have the same size and offsets as the normal sprites and are used for recolouring purposes. See the real sprites page for more info.

Example

The block contains a list of real and/or recolour sprites. An example for an implementation

 // Foster Express tram
 spriteset(foster_express_set, "opengfx_generic_trams1.pcx") {
   [ 48,56,  8,18,   -3,-10]
   [ 64,56, 20,19,  -14, -5]
   [ 96,56, 28,15,  -14, -8]
   [144,56, 20,19,   -6, -7]
   [176,56,  8,18,   -3,-10]
   [192,56, 20,19,  -14, -9]
   [224,56, 28,15,  -14, -8]
   [272,56, 20,19,   -6, -7]
 }
 
 alternative_sprites(foster_express_set, ZOOM_LEVEL_IN_2X, BIT_DEPTH_8BPP, "opengfx_generic_trams1.pcx") {
   [ 48,56,  8,18,   -3,-10]
   [ 64,56, 20,19,  -14, -5]
   [ 96,56, 28,15,  -14, -8]
   [144,56, 20,19,   -6, -7]
   [176,56,  8,18,   -3,-10]
   [192,56, 20,19,  -14, -9]
   [224,56, 28,15,  -14, -8]
   [272,56, 20,19,   -6, -7]
 }
 
 alternative_sprites(foster_express_set, ZOOM_LEVEL_NORMAL, BIT_DEPTH_32BPP, "opengfx_generic_trams1.png") {
   [ 48,56,  8,18,   -3,-10]
   [ 64,56, 20,19,  -14, -5]
   [ 96,56, 28,15,  -14, -8]
   [144,56, 20,19,   -6, -7]
   [176,56,  8,18,   -3,-10]
   [192,56, 20,19,  -14, -9]
   [224,56, 28,15,  -14, -8]
   [272,56, 20,19,   -6, -7]
 }

Advanced example with templates

Sprites for various zoom-levels and color-depths scale the number of offsets and positions you need to put into the code. This can be simplified using templates. Assume you have 3 spritesheets containing vehicle sprites for multiple vehicle and cargos, organised in rows.

  • 3 spritesheets for 8bpp 1x-zoom, 32bpp 1x-zoom, 32bpp 4x-zoom
  • Spritesheets organised in rows, one vehicle (with 8 orientations) per row
  • Rows have height 32 in 1x-spritesheet, and 128 in 4x-spritesheet.
// Template for sprites with multiple zoom levels
//  x,y    Position in 1x spritesheet
//  w,h    Size in 1x spritesheet
//  ox,oy  Offset for 1x sprite
//  zoom   Zoomlevel
template template_zoom(x, y, w, h, ox, oy, zoom) {
  [ x*zoom, y*zoom, w*zoom, h*zoom, ox*zoom, oy*zoom - (zoom/2) ]
}

// Template for a vehicle.
//  line   Line in spritesheet
//  zoom   Zoomlevel
template template_vehicle(line, zoom) {
  template_zoom(  0, line*32,  8, 18,  -3, -10, zoom) // N
  template_zoom( 16, line*32, 20, 19, -14,  -5, zoom) // NE
  template_zoom( 48, line*32, 28, 15, -14,  -8, zoom) // E
  template_zoom( 96, line*32, 20, 19,  -6,  -7, zoom) // SE
  template_zoom(128, line*32,  8, 18,  -3, -10, zoom) // S
  template_zoom(144, line*32, 20, 19, -14,  -9, zoom) // SW
  template_zoom(176, line*32, 28, 15, -14,  -8, zoom) // W
  template_zoom(224, line*32, 20, 19,  -6,  -7, zoom) // NW
}

/// Line 0 contains "coal" sprites
spriteset(vehicle_coal, "vehicles_1x_8bpp.png") {
  template_vehicle(0, 1)
}
alternative_sprites(vehicle_coal, ZOOM_LEVEL_NORMAL, BIT_DEPTH_32BPP, "vehicles_1x_32bpp.png") {
  template_vehicle(0, 1)
}
alternative_sprites(vehicle_coal, ZOOM_LEVEL_IN_4X, BIT_DEPTH_32BPP, "vehicles_4x_32bpp.png") {
  template_vehicle(0, 4)
}

/// Line 1 contains "mail" sprites
spriteset(vehicle_mail, "vehicles_1x_8bpp.png") {
  template_vehicle(1, 1)
}
alternative_sprites(vehicle_mail, ZOOM_LEVEL_NORMAL, BIT_DEPTH_32BPP, "vehicles_1x_32bpp.png") {
  template_vehicle(1, 1)
}
alternative_sprites(vehicle_mail, ZOOM_LEVEL_IN_4X, BIT_DEPTH_32BPP, "vehicles_4x_32bpp.png") {
  template_vehicle(1, 4)
}