gallium: add rasterizer depth_clamp enable bit

This is required for d3d10+, which has depth_clamp always enabled
regardless of depth_clip (in contrast to OpenGL, where enabling
depth_clamp disables depth_clip). There doesn't seem to be a GL
extension for it, but it will be used for lavapipe to implement
VK_EXT_depth_clip_enable.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12260>

docs/gallium/cso/rasterizer.rst

@@ -326,10 +326,15 @@ clip_halfz
     When true clip space in the z axis goes from [0..1] (D3D).  When false
     [-1, 1] (GL)
 
-depth_clip
-    When false, the near and far depth clipping planes of the view volume are
-    disabled and the depth value will be clamped at the per-pixel level, after
-    polygon offset has been applied and before depth testing.
+depth_clip_near
+    When false, the near depth clipping plane of the view volume is disabled.
+depth_clip_far
+    When false, the far depth clipping plane of the view volume is disabled.
+depth_clamp
+    Whether the depth value will be clamped to the interval defined by the
+    near and far depth range at the per-pixel level, after polygon offset has
+    been applied and before depth testing. Note that a clamp to [0,1] according
+    to GL rules should always happen even if this is disabled.
 
 clip_plane_enable
     For each k in [0, PIPE_MAX_CLIP_PLANES), if bit k of this field is set,

docs/gallium/screen.rst

@@ -80,6 +80,9 @@ The integer capabilities:
   disabling depth clipping (through pipe_rasterizer_state) separately for
   the near and far plane. If not, depth_clip_near and depth_clip_far will be
   equal.
+  ``PIPE_CAP_DEPTH_CLAMP_ENABLE``: Whether the driver is capable of
+  enabling depth clamping (through pipe_rasterizer_state) separately from depth
+  clipping. If not, depth_clamp will be the inverse of depth_clip_far.
 * ``PIPE_CAP_SHADER_STENCIL_EXPORT``: Whether a stencil reference value can be
   written from a fragment shader.
 * ``PIPE_CAP_TGSI_INSTANCEID``: Whether TGSI_SEMANTIC_INSTANCEID is supported

src/gallium/auxiliary/util/u_screen.c

@@ -77,6 +77,7 @@ u_pipe_screen_get_param_defaults(struct pipe_screen *pscreen,
    case PIPE_CAP_TGSI_FS_COORD_PIXEL_CENTER_INTEGER:
    case PIPE_CAP_DEPTH_CLIP_DISABLE:
    case PIPE_CAP_DEPTH_CLIP_DISABLE_SEPARATE:
+   case PIPE_CAP_DEPTH_CLAMP_ENABLE:
    case PIPE_CAP_SHADER_STENCIL_EXPORT:
    case PIPE_CAP_TGSI_INSTANCEID:
    case PIPE_CAP_VERTEX_ELEMENT_INSTANCE_DIVISOR:

src/gallium/drivers/llvmpipe/lp_screen.c

@@ -170,6 +170,8 @@ llvmpipe_get_param(struct pipe_screen *screen, enum pipe_cap param)
       return 1;
    case PIPE_CAP_DEPTH_CLIP_DISABLE:
       return 1;
+   case PIPE_CAP_DEPTH_CLAMP_ENABLE:
+      return 1;
    case PIPE_CAP_SHADER_STENCIL_EXPORT:
       return 1;
    case PIPE_CAP_TGSI_INSTANCEID:

src/gallium/drivers/llvmpipe/lp_state_fs.c

@@ -4165,10 +4165,8 @@ make_variant_key(struct llvmpipe_context *lp,
 
    /*
     * Propagate the depth clamp setting from the rasterizer state.
-    * depth_clip == 0 implies depth clamping is enabled.
-    *
     */
-   key->depth_clamp = (lp->rasterizer->depth_clip_near == 0) ? 1 : 0;
+   key->depth_clamp = lp->rasterizer->depth_clamp;
 
    /* alpha test only applies if render buffer 0 is non-integer (or does not exist) */
    if (!lp->framebuffer.nr_cbufs ||

src/gallium/frontends/d3d10umd/Rasterizer.cpp

@@ -226,6 +226,7 @@ CreateRasterizerState(
    state.clip_halfz = 1;
    state.depth_clip_near = pRasterizerDesc->DepthClipEnable ? 1 : 0;
    state.depth_clip_far = pRasterizerDesc->DepthClipEnable ? 1 : 0;
+   state.depth_clamp = 1;
 
    state.point_quad_rasterization = 1;
    state.point_size = 1.0f;

src/gallium/include/pipe/p_defines.h

@@ -764,6 +764,7 @@ enum pipe_cap
    PIPE_CAP_TGSI_FS_COORD_PIXEL_CENTER_INTEGER,
    PIPE_CAP_DEPTH_CLIP_DISABLE,
    PIPE_CAP_DEPTH_CLIP_DISABLE_SEPARATE,
+   PIPE_CAP_DEPTH_CLAMP_ENABLE,
    PIPE_CAP_SHADER_STENCIL_EXPORT,
    PIPE_CAP_TGSI_INSTANCEID,
    PIPE_CAP_VERTEX_ELEMENT_INSTANCE_DIVISOR,

src/gallium/include/pipe/p_state.h

@@ -162,6 +162,13 @@ struct pipe_rasterizer_state
    unsigned depth_clip_near:1;
    unsigned depth_clip_far:1;
 
+   /**
+    * When true, depth clamp is enabled.
+    * If PIPE_CAP_DEPTH_CLAMP_ENABLE is unsupported, this is always the inverse
+    * of depth_clip_far.
+    */
+   unsigned depth_clamp:1;
+
    /**
     * When true clip space in the z axis goes from [0..1] (D3D).  When false
     * [-1, 1] (GL).

src/mesa/state_tracker/st_atom_rasterizer.c

@@ -300,6 +300,7 @@ st_update_rasterizer(struct st_context *st)
                              !ctx->Transform.DepthClampNear;
    raster->depth_clip_far = st->clamp_frag_depth_in_shader ||
                             !ctx->Transform.DepthClampFar;
+   raster->depth_clamp = !raster->depth_clip_far;
    raster->clip_plane_enable = ctx->Transform.ClipPlanesEnabled;
    raster->clip_halfz = (ctx->Transform.ClipDepthMode == GL_ZERO_TO_ONE);
 

src/mesa/state_tracker/st_cb_drawpixels.c

@@ -789,6 +789,7 @@ draw_textured_quad(struct gl_context *ctx, GLint x, GLint y, GLfloat z,
                                    !ctx->Transform.DepthClampNear;
       rasterizer.depth_clip_far = st->clamp_frag_depth_in_shader ||
                                   !ctx->Transform.DepthClampFar;
+      rasterizer.depth_clamp = !rasterizer.depth_clip_far;
       rasterizer.scissor = ctx->Scissor.EnableFlags;
       cso_set_rasterizer(cso, &rasterizer);
    }