graphics/image: add load-image-from-memory (decode encoded bytes) for web

Message

On the web there is no filesystem, so load-image's stbiload(path) can't be used. Add (load-image-from-memory ptr len): decode an image from raw encoded bytes already resident in linear memory (a wasm address + length), via stbimage's stbiloadfrom_memory, producing the same <image> object load-image returns from a path. The web build's sigil-wasm-gles3 app-shell fetches the file and copies its bytes into memory; this turns them into a GPU texture.

Purely ADDITIVE: a new procedure on native + web alike (stbiloadfrommemory is core stbimage). It changes no existing behaviour and removes no lines; it is exported unconditionally because the module's (export) list must match the C registration on both platforms. Native image.c compiles unchanged.

Changed

 src/c/image.c                | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/sigil/graphics/image.sgl |  1 +
 2 files changed, 53 insertions(+)

Diff

src/c/image.cmodified

@@ -98,6 +98,55 @@ static Value native_load_image(SigilVM *vm, int argc, Value *args)

sizeof(StudioImage) + (size_t)(width * height * 4));

}

100

+101

/*

+102

* (load-image-from-memory ptr len) -> <image> or #f

+103

*

+104

* Decode an image from raw ENCODED bytes already resident in WASM linear memory

+105

* at address `ptr` (a fixnum), `len` bytes long, using stb_image's from-memory

+106

* decoder. On web there is no filesystem: JS fetches the image file and copies

+107

* the encoded bytes into memory (see the sigil-wasm-gles3 app-shell), and this

+108

* turns them into the same <image> object load-image produces from a path.

+109

*

+110

* ADDITIVE: a new procedure available on native + web alike. It changes no

+111

* existing behaviour (stbi_load_from_memory is core stb_image); it is exported

+112

* unconditionally because the module's (export) list must match the C

+113

* registration on both platforms.

+114

*/

+115

static Value native_load_image_from_memory(SigilVM *vm, int argc, Value *args)

+116

{

+117

(void)argc;

+118

+119

if (!sigil_is_fixnum(args[0]) || !sigil_is_fixnum(args[1])) {

+120

sigil__vm_set_error(vm, SIGIL_ERR_TYPE,

+121

"load-image-from-memory: expected (ptr len) fixnums");

+122

return SIGIL_FALSE;

+123

}

+124

+125

const unsigned char *bytes = (const unsigned char *)(uintptr_t)sigil_as_fixnum(args[0]);

+126

int len = (int)sigil_as_fixnum(args[1]);

+127

if (!bytes || len <= 0) return SIGIL_FALSE;

+128

+129

int width, height, channels;

+130

unsigned char *pixels = stbi_load_from_memory(bytes, len, &width, &height, &channels, 4);

+131

if (!pixels) return SIGIL_FALSE;

+132

+133

StudioImage *img = malloc(sizeof(StudioImage));

+134

if (!img) {

+135

stbi_image_free(pixels);

+136

sigil__vm_set_error(vm, SIGIL_ERR_MEMORY, "load-image-from-memory: out of memory");

+137

return SIGIL_FALSE;

+138

}

+139

+140

img->pixels = pixels;

+141

img->width = width;

+142

img->height = height;

+143

img->channels = 4;

+144

+145

ensure_image_type(vm);

+146

return sigil_make_foreign(vm, image_type_tag, img, image_destructor,

+147

sizeof(StudioImage) + (size_t)(width * height * 4));

+148

}

+149

150

/*

151

* (image? obj) -> boolean

152

*

@@ -214,6 +263,8 @@ void sigil__init_sigil_graphics_image_module(SigilVM *vm)

263

264

sigil_module_register_native(vm, "load-image", native_load_image,

265

SIGIL_ARITY_EXACT(1), "Load image from file path");

+266

sigil_module_register_native(vm, "load-image-from-memory", native_load_image_from_memory,

+267

SIGIL_ARITY_EXACT(2), "Decode an image from encoded bytes in memory");

268

sigil_module_register_native(vm, "image?", native_image_p,

269

SIGIL_ARITY_EXACT(1), "Check if object is an image");

270

sigil_module_register_native(vm, "image-width", native_image_width,

@@ -226,6 +277,7 @@ void sigil__init_sigil_graphics_image_module(SigilVM *vm)

277

SIGIL_ARITY_EXACT(1), "Free image pixel data");

278

279

sigil_module_export(vm, "load-image");

+280

sigil_module_export(vm, "load-image-from-memory");

281

sigil_module_export(vm, "image?");

282

sigil_module_export(vm, "image-width");

283

sigil_module_export(vm, "image-height");

src/sigil/graphics/image.sglmodified

@@ -13,6 +13,7 @@

(export

;; Image loading

load-image

+16

load-image-from-memory

;; Image predicates and properties

image?