hey! I've noticed there weren't any good examples for drawing an *image* with Citro2D. spritesheets and t3x files, sure!
anyways, I want to share what I learnt from digging around other homebrew projects for someone in a similar position to me ^w^.
here is a snippet from git DOT sr DOT ht/~sheepy/c2d-image-example/ @ source/main.c! check out the README.md in that repo for a rust3ds version, too.
anyway, I'm hoping this can help someone out. It's a *lot* faster than writing to the fb manually, & useful for cases where you can't just use a spritesheet (e.g. album art).
anyways, I want to share what I learnt from digging around other homebrew projects for someone in a similar position to me ^w^.
here is a snippet from git DOT sr DOT ht/~sheepy/c2d-image-example/ @ source/main.c! check out the README.md in that repo for a rust3ds version, too.
C:
const u32 next_pow2(u32 n) {
n--;
n |= n >> 1;
n |= n >> 2;
n |= n >> 4;
n |= n >> 8;
n |= n >> 16;
n++;
return n;
}
const u32 clamp(u32 n, u32 lower, u32 upper) {
if (n < lower)
return lower;
if (n > upper)
return upper;
return n;
}
const u32 rgba_to_abgr(u32 px) {
u8 r = (px & 0xff000000) >> 24;
u8 g = (px & 0x00ff0000) >> 16;
u8 b = (px & 0x0000ff00) >> 8;
u8 a = px & 0x000000ff;
return (a << 24) | (b << 16) | (g << 8) | r;
}
/** Read an RGBA image from `path` with dimensions `image_width`x`image_height`
* and return a `C2D_Image` object.
* Assumes image data is stored left->right, top->bottom.
* Dimensions must be within 64x64 and 1024x1024.
* svcBreak's if the file can't be opened. */
C2D_Image get_image(const char *path, u32 image_width, u32 image_height) {
// Open file
FILE *file = fopen(path, "rb");
if (file == NULL) {
fprintf(stderr, "failed to open `%s'", path);
svcBreak(USERBREAK_PANIC);
}
u32 px_count = image_width * image_height;
u32 *rgba_raw = malloc(px_count * sizeof(u32));
fread((char *)rgba_raw, sizeof(u32), px_count, file);
// Image data
C2D_Image image;
// Base texture
C3D_Tex *tex = malloc(sizeof(C3D_Tex));
image.tex = tex;
// Texture dimensions must be square powers of two between 64x64 and 1024x1024
tex->width = clamp(next_pow2(image_width), 64, 1024);
tex->height = clamp(next_pow2(image_height), 64, 1024);
// Subtexture
Tex3DS_SubTexture *subtex = malloc(sizeof(Tex3DS_SubTexture));
image.subtex = subtex;
subtex->width = image_width;
subtex->height = image_height;
// (U, V) coordinates
subtex->left = 0.0f;
subtex->top = 1.0f;
subtex->right = (float)image_width / (float)tex->width;
subtex->bottom = 1.0 - ((float)image_height / (float)tex->height);
C3D_TexInit(tex, tex->width, tex->height, GPU_RGBA8);
C3D_TexSetFilter(tex, GPU_LINEAR, GPU_NEAREST);
memset(tex->data, 0, px_count * 4);
for (u8 i = 0; i < image_height; i++) {
for (u8 j = 0; j < image_width; j++) {
u32 src_idx = (j * image_width) + i;
u32 rgba_px = rgba_raw[src_idx];
u32 abgr_px = rgba_to_abgr(rgba_px);
// 8x8 Morton Z-order swizzling, c.f.
// https://problemkaputt.de/gbatek-3ds-video-texture-swizzling.htm
// https://github.com/astronautlevel2/Anemone3DS/blob/ba08ab9108cec81a4fcb31d12a2af09bab589b82/source/loading.c#L338
// https://github.com/devkitPro/tex3ds/blob/master/source/swizzle.cpp
u32 dst_ptr_offset = ((((j >> 3) * (tex->width >> 3) + (i >> 3)) << 6) +
((i & 1) | ((j & 1) << 1) | ((i & 2) << 1) |
((j & 2) << 2) | ((i & 4) << 2) | ((j & 4) << 3)));
((u32 *)tex->data)[dst_ptr_offset] = abgr_px;
}
}
free(rgba_raw);
return image;
}anyway, I'm hoping this can help someone out. It's a *lot* faster than writing to the fb manually, & useful for cases where you can't just use a spritesheet (e.g. album art).
Last edited by sheepy0125,
).
. bwuh.
