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Tilemaps can have two objects placed on it, 'p_foreground' and 'p_vanishing' whose placement form a virtual perspective plane, which causes sprites to scale as they move up and down the screen between them, creating the illusion of depth on the screen

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This commit is contained in:
Andrew Kesterson
2026-05-13 09:57:24 -04:00
parent b8dee456ca
commit 53e4f5c14f
6 changed files with 87 additions and 28 deletions
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9
src/actor.c
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@@ -254,8 +254,8 @@ akerr_ErrorContext *akgl_actor_render(akgl_Actor *obj, SDL_Renderer *renderer)
dest.x = (obj->x - camera.x);
dest.y = (obj->y - camera.y);
}
dest.w = curSprite->width;
dest.h = curSprite->width;
dest.w = curSprite->width * obj->scale;
dest.h = curSprite->width * obj->scale;
SDL_RenderTexture(renderer, curSprite->sheet->texture, &src, &dest);
SUCCEED_RETURN(errctx);
@@ -300,6 +300,11 @@ void akgl_registry_iterate_actor(void *userdata, SDL_PropertiesID registry, cons
if ( AKGL_BITMASK_HAS(opflags->flags, AKGL_ITERATOR_OP_UPDATE) ) {
CATCH(errctx, obj->updatefunc(obj));
}
if ( AKGL_BITMASK_HAS(opflags->flags, AKGL_ITERATOR_OP_TILEMAPSCALE) ) {
CATCH(errctx, akgl_tilemap_scale_actor(&gamemap, obj));
} else {
obj->scale = 1.0;
}
if ( AKGL_BITMASK_HAS(opflags->flags, AKGL_ITERATOR_OP_RENDER) ) {
CATCH(errctx, obj->renderfunc(obj, renderer));
}

49
src/tilemap.c
View File

@@ -272,12 +272,22 @@ akerr_ErrorContext *akgl_tilemap_load_layer_objects(akgl_Tilemap *dest, json_t *
CATCH(errctx, akgl_heap_release_string(tmpstr));
CATCH(errctx, akgl_get_json_number_value((json_t *)layerdatavalue, "x", &curobj->x));
CATCH(errctx, akgl_get_json_number_value((json_t *)layerdatavalue, "y", &curobj->y));
CATCH(errctx, akgl_get_json_boolean_value((json_t *)layerdatavalue, "visible", &curobj->visible));
CATCH(errctx, akgl_get_json_boolean_value((json_t *)layerdatavalue, "visible", &curobj->visible));
CATCH(errctx, akgl_get_json_string_value((json_t *)layerdatavalue, "type", &tmpstr));
if ( strcmp(tmpstr->data, "actor") == 0 ) {
CATCH(errctx, akgl_tilemap_load_layer_object_actor(curobj, layerdatavalue, layerid));
} else if ( strcmp(tmpstr->data, "perspective") == 0 ) {
curobj->visible = false;
if ( strcmp((char *)curobj->name, "p_foreground") == 0 ) {
dest->p_foreground_y = curobj->y;
CATCH(errctx, akgl_get_json_integer_value((json_t *)layerdatavalue, "height", &dest->p_foreground_h));
} else if ( strcmp((char *)curobj->name, "p_vanishing") == 0 ) {
dest->p_vanishing_y = curobj->y;
CATCH(errctx, akgl_get_json_integer_value((json_t *)layerdatavalue, "height", &dest->p_vanishing_h));
}
}
layerdatavalue = NULL;
}
} CLEANUP {
@@ -436,6 +446,21 @@ akerr_ErrorContext *akgl_tilemap_load(char *fname, akgl_Tilemap *dest)
CATCH(errctx, akgl_tilemap_load_layers((akgl_Tilemap *)dest, (json_t *)json));
CATCH(errctx, akgl_tilemap_load_tilesets((akgl_Tilemap *)dest, (json_t *)json));
if ( dest->p_foreground_y && dest->p_vanishing_y ) {
// How much bigger is the foreground vs the vanishing point?
// if vanishing is height 16, and foreground is height 32, that is a 2x scale difference
dest->p_scale = (dest->p_foreground_h / dest->p_vanishing_h);
SDL_Log("Map perspective scale is (%f/%f) = %f", dest->p_foreground_h, dest->p_vanishing_h, dest->p_scale);
// Sprites are always size 1.0 at the foreground, so how much do we need to
// scale them for every pixel above foreground_y before they reach vanishing_y?
// If vanishing is at 320 and foreground is at 640, that is a 320 line difference
// If our scaling rate is 2x, then our rate is ((1.0 - (1.0 / 2.0)) / 320.0), or
// 0.0015625% scale per pixel.
// At position 640,
dest->p_rate = (1.0 / (dest->p_foreground_y - dest->p_vanishing_y)) / dest->p_scale;
SDL_Log("Map perspective rate is %f", dest->p_rate);
}
} CLEANUP {
//IGNORE(akgl_heap_release_string(tmpstr));
} PROCESS(errctx) {
@@ -613,3 +638,25 @@ akerr_ErrorContext *akgl_tilemap_draw_tileset(SDL_Renderer *renderer, akgl_Tilem
}
SUCCEED_RETURN(errctx);
}
akerr_ErrorContext AKERR_NOIGNORE *akgl_tilemap_scale_actor(akgl_Tilemap *map, akgl_Actor *actor)
{
PREPARE_ERROR(e);
FAIL_ZERO_RETURN(e, map, AKERR_NULLPOINTER, "NULL map");
FAIL_ZERO_RETURN(e, actor, AKERR_NULLPOINTER, "NULL actor");
SDL_Log("Map foreground is at %d, vanishes at %d, actor %p is at %f",
map->p_foreground_y,
map->p_vanishing_y,
actor,
actor->y);
if ( actor->y <= map->p_vanishing_y ) {
actor->scale = 1.0 / map->p_scale;
} else if ( actor->y >= map->p_foreground_y ) {
actor->scale = 1.0;
} else {
actor->scale = 1.0 - (map->p_rate * (map->p_foreground_y - actor->y));
}
SDL_Log("Actor %p scaled to %f", actor, actor->scale);
}