vkd3d-shader/ir: Allow controlling FFP point size clamping through vkd3d-shader parameters.

Approved-by: Henri Verbeet (@hverbeet)
Merge-Request: https://gitlab.winehq.org/wine/vkd3d/-/merge_requests/1146

include/vkd3d_shader.h

@@ -667,6 +667,39 @@ enum vkd3d_shader_parameter_name
      * \since 1.14
      */
     VKD3D_SHADER_PARAMETER_NAME_POINT_SIZE,
+    /**
+     * Minimum point size.
+     *
+     * When this parameter is provided to a vertex, tessellation, or geometry
+     * shader, and the source shader writes point size or uses the
+     * VKD3D_SHADER_PARAMETER_NAME_POINT_SIZE parameter, the point size will
+     * be clamped to the provided minimum value.
+     * If point size is not written in one of these ways,
+     * this parameter is ignored.
+     * If this parameter is not provided, the point size will not be clamped
+     * to a minimum size by vkd3d-shader.
+     *
+     * This parameter can be used to implement fixed function point size, as
+     * present in Direct3D versions 8 and 9, if the target environment does not
+     * support point size as part of its own fixed-function API (as Vulkan and
+     * core OpenGL).
+     *
+     * The data type for this parameter must be
+     * VKD3D_SHADER_PARAMETER_DATA_TYPE_FLOAT32.
+     *
+     * \since 1.14
+     */
+    VKD3D_SHADER_PARAMETER_NAME_POINT_SIZE_MIN,
+    /**
+     * Maximum point size.
+     *
+     * This parameter has identical behaviour to
+     * VKD3D_SHADER_PARAMETER_NAME_POINT_SIZE_MIN, except that it provides
+     * the maximum size rather than the minimum.
+     *
+     * \since 1.14
+     */
+    VKD3D_SHADER_PARAMETER_NAME_POINT_SIZE_MAX,
 
     VKD3D_FORCE_32_BIT_ENUM(VKD3D_SHADER_PARAMETER_NAME),
 };