`gba::object_affine` Reference

gba::object_affine is the affine OAM object entry type from <gba/video>.

Use it with gba::obj_aff_mem when sprite rotation/scaling (OBJ affine transform) is required.

For regular objects with flip bits, see gba::object.

Include

#include <gba/video>

Type summary

struct object_affine {
    // Attribute 0
    unsigned short y : 8;
    bool affine : 1 = true;
    bool double_size : 1;
    gba::mode mode : 2;
    bool mosaic : 1;
    gba::depth depth : 1;
    gba::shape shape : 2;

    // Attribute 1
    unsigned short x : 9;
    unsigned short affine_index : 5;
    unsigned short size : 2;

    // Attribute 2
    unsigned short tile_index : 10;
    unsigned short background : 2;
    unsigned short palette_index : 4;
};

sizeof(gba::object_affine) == 6 bytes.

Typical usage

gba::obj_aff_mem[0] = {
    .y = 80,
    .x = 120,
    .affine_index = 0,
    .shape = gba::shape_square,
    .size = 1,
    .depth = gba::depth_4bpp,
    .tile_index = 0,
};

// Configure affine matrix 0 through mem_obj_affa/b/c/d as needed.

Field notes

affine: set for affine rendering mode (enabled by default in the struct).
double_size: doubles the render box so rotated/scaled sprites are less likely to clip.
affine_index: selects one of 32 affine parameter sets (0..31).
shape + size: still determine the base dimensions before affine transform.
flip_x/flip_y do not exist on affine entries; transform comes from the affine matrix.

Affine parameter memory

<gba/video> provides these typed views over OAM affine parameters:

gba::mem_obj_affa (pa)
gba::mem_obj_affb (pb)
gba::mem_obj_affc (pc)
gba::mem_obj_affd (pd)

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