SPR

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← Half-Life SDK

.SPR is a file format used to store 2D sprites in GoldSrc. It is a modified version of the SPR format used by Quake, adding a dedicated color palette and additional translucency formats (Quake SPRs only support alphatest transparency).

SPR files are technically considered models by the game code and engine. As such, any entity which displays a sprite can be made to display a MDL or external BSP by simply changing the file path.

Limitations

Warning:All frames in a multi-frame sprite share the same palette.

Bug:Oriented sprites are finicky; see The303's tutorials for more information.

Bug:Sprites being displayed via env_glow cannot be oriented in the map editor. If rotation is necessary, use env_sprite instead.

Image format types

Format	Explanation
Normal	Opaque image with no transparency
Additive	Same as Normal; Additive translucency can be achieved for any image format by changing the sprite's rendermode (either in a sprite entity, or via code)
IndexAlpha	Single-color with 8-bit translucency
AlphaTest	Binary alpha-tested transparency; pixels using the last color in the palette will be transparent

Orientation types

Orientation	Explaination
Parallel	Rotates to always face the camera
Parallel Upright	Like parallel, but doesn't rotate around Z axis
Oriented	Rotated in map editor to face a specific direction
Parallel Oriented	Combination of parallel and oriented.
Facing Upright	Like parallel upright, but rotated based on player origin, rather than camera.

Technical

Header

struct sprite
{
    int         id;             // format ID, "IDSP" (0x49 0x44 0x53 0x50)
    int         version;        // Format version number. HL1 SPRs are version 2 (0x02,0x00,0x00,0x00)
    int         spriteType;     // Orientation method
    int         textFormat;     // Translucency/Transparency method
    float       boundingRadius;
    int         maxWidth;
    int         maxHeight;
    int         frameNum;          // number of frames the sprite contains
    float       beamLength;
    int         synchType;

    short       paletteColorCount; // number of colors in the palette; should be 256
};

Palette

After the header, comes a list of palette colors of "paletteColorCount" size, each one 3 bytes - Red, Green, Blue.

Frames

After that come the sprite frames. (frameNum from the header)

struct sprite_frame_header
{
    int         group;            
    int         originX;        // not sure about this one, it always huge for sprites in HL1
    int         originY;
    int         width;
    int         height;

    // Right after this, the paletted image data comes, each byte is a pixel.
    // The image size is given in the frame header, so the entire data for 1 frame is width*height bytes.
};

External links

• GoldSrc Sprite Tutorial by The303