Cache transform buffer to reduce per-frame malloc

This implements transform buffer cache in twin_pixmap_t to eliminate
malloc and free on every transform compositing operation. Previous code
allocated and freed the xform buffer for each transformation, creating
unnecessary allocation overhead in the render loop.

Author: jserv

include/twin.h

@@ -253,6 +253,10 @@ typedef struct _twin_pixmap {
 #endif
 
     twin_window_t *window; /**< Associated window (if any) */
+
+    /* Transform buffer cache for compositing operations */
+    void *xform_cache;       /**< Cached xform buffer */
+    size_t xform_cache_size; /**< Cached xform buffer size in bytes */
 } twin_pixmap_t;
 
 /**

src/draw-builtin.c

@@ -633,10 +633,22 @@ static twin_xform_t *twin_pixmap_init_xform(twin_pixmap_t *pixmap,
     if (fmt == TWIN_RGB16)
         fmt = TWIN_ARGB32;
 
-    twin_xform_t *xform =
-        calloc(1, sizeof(twin_xform_t) + width * twin_bytes_per_pixel(fmt));
-    if (!xform)
-        return NULL;
+    size_t required_size =
+        sizeof(twin_xform_t) + (size_t) width * twin_bytes_per_pixel(fmt);
+
+    /* Reuse cached xform buffer if large enough */
+    twin_xform_t *xform;
+    if (pixmap->xform_cache && pixmap->xform_cache_size >= required_size) {
+        xform = (twin_xform_t *) pixmap->xform_cache;
+    } else {
+        /* Need larger cache - reallocate */
+        void *new_cache = realloc(pixmap->xform_cache, required_size);
+        if (!new_cache)
+            return NULL;
+        pixmap->xform_cache = new_cache;
+        pixmap->xform_cache_size = required_size;
+        xform = (twin_xform_t *) new_cache;
+    }
 
     xform->span.v = (twin_argb32_t *) (char *) (xform + 1);
     xform->pixmap = pixmap;
@@ -650,7 +662,9 @@ static twin_xform_t *twin_pixmap_init_xform(twin_pixmap_t *pixmap,
 
 static void twin_pixmap_free_xform(twin_xform_t *xform)
 {
-    free(xform);
+    /* Xform buffer is now cached in pixmap - don't free */
+    /* This function is kept for API compatibility but does nothing */
+    (void) xform;
 }
 
 #define FX(x) twin_int_to_fixed(x)

src/pixmap.c

@@ -52,6 +52,8 @@ twin_pixmap_t *twin_pixmap_create(twin_format_t format,
     pixmap->shadow = false;
 #endif
     pixmap->window = NULL; /* Initialize window field */
+    pixmap->xform_cache = NULL;
+    pixmap->xform_cache_size = 0;
     pixmap->p.v = pixmap + 1;
     memset(pixmap->p.v, '\0', space);
     return pixmap;
@@ -82,6 +84,8 @@ twin_pixmap_t *twin_pixmap_create_const(twin_format_t format,
     pixmap->stride = stride;
     pixmap->disable = 0;
     pixmap->window = NULL; /* Initialize window field */
+    pixmap->xform_cache = NULL;
+    pixmap->xform_cache_size = 0;
     pixmap->p = pixels;
     return pixmap;
 }
@@ -90,6 +94,7 @@ void twin_pixmap_destroy(twin_pixmap_t *pixmap)
 {
     if (pixmap->screen)
         twin_pixmap_hide(pixmap);
+    free(pixmap->xform_cache); /* Free xform buffer cache */
     free(pixmap);
 }