Separated BlenderRenderCommand into an abstract superclass

This superclass AbstractBlenderCommand takes less parameters so that it'll
be easier to add Blender commands that don't use certain parameters (such
as frame range, render format, etc.)

flamenco_worker/commands.py

@@ -666,8 +666,7 @@ class ExecCommand(AbstractSubprocessCommand):
         await self.subprocess(shlex.split(settings['cmd']))
 
 
-@command_executor('blender_render')
-class BlenderRenderCommand(AbstractSubprocessCommand):
+class AbstractBlenderCommand(AbstractSubprocessCommand):
     re_global_progress = attr.ib(init=False)
     re_time = attr.ib(init=False)
     re_remaining = attr.ib(init=False)
@@ -709,23 +708,6 @@ class BlenderRenderCommand(AbstractSubprocessCommand):
             return 'blender_cmd %r does not exist' % cmd[0]
         settings['blender_cmd'] = cmd
 
-        render_output, err = self._setting(settings, 'render_output', False)
-        if err:
-            return err
-        if render_output:
-            outpath = Path(render_output).parent
-            try:
-                outpath.mkdir(parents=True, exist_ok=True)
-            except Exception as ex:
-                return '"render_output": dir %s cannot be created: %s' % (outpath, ex)
-
-        _, err = self._setting(settings, 'frames', False)
-        if err:
-            return err
-        _, err = self._setting(settings, 'render_format', False)
-        if err:
-            return err
-
         filepath, err = self._setting(settings, 'filepath', True)
         if err:
             return err
@@ -779,14 +761,6 @@ class BlenderRenderCommand(AbstractSubprocessCommand):
                     '--python', override_filepath.as_posix(),
                 ])
 
-        if settings.get('python_expr'):
-            cmd.extend(['--python-expr', settings['python_expr']])
-        if settings.get('render_output'):
-            cmd.extend(['--render-output', settings['render_output']])
-        if settings.get('format'):
-            cmd.extend(['--render-format', settings['format']])
-        if settings.get('frames'):
-            cmd.extend(['--render-frame', settings['frames']])
         return cmd
 
     def parse_render_line(self, line: str) -> typing.Optional[dict]:
@@ -865,6 +839,43 @@ class BlenderRenderCommand(AbstractSubprocessCommand):
         return 'pid=%d > %s' % (self.proc.pid, line)
 
 
+@command_executor('blender_render')
+class BlenderRenderCommand(AbstractBlenderCommand):
+
+    def validate(self, settings: Settings):
+        render_output, err = self._setting(settings, 'render_output', False)
+        if err:
+            return err
+        if render_output:
+            outpath = Path(render_output).parent
+            try:
+                outpath.mkdir(parents=True, exist_ok=True)
+            except Exception as ex:
+                return '"render_output": dir %s cannot be created: %s' % (outpath, ex)
+
+        _, err = self._setting(settings, 'frames', False)
+        if err:
+            return err
+        _, err = self._setting(settings, 'render_format', False)
+        if err:
+            return err
+
+        return super().validate(settings)
+
+    async def _build_blender_cmd(self, settings) -> typing.List[str]:
+        cmd = await super()._build_blender_cmd(settings)
+
+        if settings.get('python_expr'):
+            cmd.extend(['--python-expr', settings['python_expr']])
+        if settings.get('render_output'):
+            cmd.extend(['--render-output', settings['render_output']])
+        if settings.get('format'):
+            cmd.extend(['--render-format', settings['format']])
+        if settings.get('frames'):
+            cmd.extend(['--render-frame', settings['frames']])
+        return cmd
+
+
 @command_executor('blender_render_progressive')
 class BlenderRenderProgressiveCommand(BlenderRenderCommand):
     def validate(self, settings: Settings):
@@ -995,6 +1006,7 @@ class MergeProgressiveRendersCommand(AbstractSubprocessCommand):
         shutil.move(str(src), str(dst))
 
 
+# TODO(Sybren): maybe subclass AbstractBlenderCommand instead?
 @command_executor('blender_render_audio')
 class BlenderRenderAudioCommand(BlenderRenderCommand):
     def validate(self, settings: Settings):