vo_gpu: add support for DEFINE parameters

DOCS/man/options.rst

@@ -6445,8 +6445,10 @@ them.
         Parameters are global across the entire shader file, all hooks in the
         file can reference them, regardless of declaration order.
 
-    TYPE <type> (required)
+    TYPE <DEFINE | <type>> (required)
         The parameter type. Supported types are ``float`` and ``int``.
+        The special type ``DEFINE`` emits a preprocessor define which can be
+        used inside ``#if`` directives.
 
     MINIMUM <value>
         Minimum allowed value for this parameter.
@@ -6464,7 +6466,7 @@ them.
         ``vo=gpu`` supports only a subset of the parameter features available in
         ``vo=gpu-next``. See libplacebo documentation for more detailed
         information about PARAM features supported in ``vo=gpu-next``. Notably
-        ``uint``, ``ENUM``, ``DEFINE``, ``DYNAMIC``, and ``CONSTANT`` types are
+        ``uint``, ``ENUM``, ``DYNAMIC``, and ``CONSTANT`` types are
         not available, and parameters cannot be referenced in ``WHEN``
         expression.
 

video/out/gpu/user_shaders.c

@@ -36,6 +36,7 @@ bool parse_shader_param_value(struct mp_log *log, struct gl_user_shader_param *p
         mp_err(log, "Missing type for param '%.*s'\n", BSTR_P(param->name));
         return false;
     case GL_USER_SHADER_PARAM_INT:
+    case GL_USER_SHADER_PARAM_DEFINE:
         v = bstrtoll(val, &rest, 10);
         range[0] = INT_MIN;
         range[1] = INT_MAX;
@@ -136,6 +137,8 @@ static bool parse_param(struct mp_log *log, struct bstr *body,
                 param->type = GL_USER_SHADER_PARAM_FLOAT;
             } else if (bstr_equals0(line, "int")) {
                 param->type = GL_USER_SHADER_PARAM_INT;
+            } else if (bstr_equals0(line, "DEFINE")) {
+                param->type = GL_USER_SHADER_PARAM_DEFINE;
             } else {
                 mp_err(log, "Unrecognized PARAM TYPE: '%.*s'!\n", BSTR_P(line));
                 return false;

video/out/gpu/user_shaders.h

@@ -67,6 +67,7 @@ enum gl_user_shader_param_type {
     GL_USER_SHADER_PARAM_UNKNOWN,
     GL_USER_SHADER_PARAM_FLOAT,
     GL_USER_SHADER_PARAM_INT,
+    GL_USER_SHADER_PARAM_DEFINE,
 };
 
 struct gl_user_shader_param {

video/out/gpu/video.c

@@ -2211,6 +2211,9 @@ static void user_hook(struct gl_video *p, struct image img,
         case GL_USER_SHADER_PARAM_INT:
             gl_sc_uniform_i_bstr(p->sc, param->name, lrint(value));
             break;
+        case GL_USER_SHADER_PARAM_DEFINE:
+            GLSLHF("#define %.*s %d\n", BSTR_P(param->name), (int)lrint(value));
+            break;
         }
     }