util: Move fetch_rgba to a separate function table.

Only llvmpipe and translate_generic use it, and only in fallbacks, so if
you're not building that then let's not bloat our binaries with it.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6305>

src/util/format/u_format.h

@@ -345,14 +345,6 @@ struct util_format_unpack_description {
                   const uint8_t *src, unsigned src_stride,
                   unsigned width, unsigned height);
 
-   /**
-    * Fetch a single pixel (i, j) from a block.
-    *
-    * Only defined for non-depth-stencil and non-integer formats.
-    */
-   void
-   (*fetch_rgba)(void *dst, const uint8_t *src, unsigned i, unsigned j);
-
    /**
     * Unpack pixels to Z32_UNORM.
     * Note: strides are in bytes.
@@ -387,6 +379,9 @@ struct util_format_unpack_description {
                      unsigned width, unsigned height);
 };
 
+typedef void (*util_format_fetch_rgba_func_ptr)(void *dst, const uint8_t *src,
+                                                unsigned i, unsigned j);
+
 const struct util_format_description *
 util_format_description(enum pipe_format format) ATTRIBUTE_CONST;
 
@@ -396,6 +391,13 @@ util_format_pack_description(enum pipe_format format) ATTRIBUTE_CONST;
 const struct util_format_unpack_description *
 util_format_unpack_description(enum pipe_format format) ATTRIBUTE_CONST;
 
+/**
+ * Returns a function to fetch a single pixel (i, j) from a block.
+ *
+ * Only defined for non-depth-stencil and non-integer formats.
+ */
+util_format_fetch_rgba_func_ptr
+util_format_fetch_rgba_func(enum pipe_format format) ATTRIBUTE_CONST;
 
 /*
  * Format query functions.

src/util/format/u_format_table.py

@@ -174,6 +174,17 @@ def write_format_table(formats):
         print("}")
         print()
 
+    def generate_function_getter(func):
+        print("util_format_%s_func_ptr" % func)
+        print("util_format_%s_func(enum pipe_format format)" % (func))
+        print("{")
+        print("   if (format >= ARRAY_SIZE(util_format_%s_table))" % (func))
+        print("      return NULL;")
+        print()
+        print("   return util_format_%s_table[format];" % (func))
+        print("}")
+        print()
+
     print('static const struct util_format_description')
     print('util_format_descriptions[] = {')
     for format in formats:
@@ -240,8 +251,6 @@ def write_format_table(formats):
             continue
 
         print("   [%s] = {" % (format.name,))
-        if format.colorspace != ZS:
-            print("      .fetch_rgba = &util_format_%s_fetch_rgba," % sn)
 
         if format.colorspace != ZS and not format.is_pure_color():
             print("      .unpack_rgba_8unorm = &util_format_%s_unpack_rgba_8unorm," % sn)
@@ -266,6 +275,20 @@ def write_format_table(formats):
 
     generate_table_getter("unpack_")
 
+    print('static const util_format_fetch_rgba_func_ptr util_format_fetch_rgba_table[] = {')
+    for format in formats:
+        sn = format.short_name()
+
+        if format.colorspace != ZS and has_access(format):
+            print("  [%s] = &util_format_%s_fetch_rgba," % (format.name, sn))
+        else:
+            print("  [%s] = NULL," % format.name)
+
+    print("};")
+    print()
+
+    generate_function_getter("fetch_rgba")
+
 def main():
     formats = []