[Mesa-dev] [PATCH v2] i965: do not round line width when multisampling or antialiaing are enabled

[Iago Toral Quiroga]

In commit fe74fee8fa721a we rounded the line width to the nearest integer to
match the GLES3 spec requirements stated in section 13.4.2.1, but that seems
to break a dEQP test that renders wide lines in some multisampling scenarios.

Ian noted that the Open 4.4 spec has the following similar text:

    "The actual width of non-antialiased lines is determined by rounding the
    supplied width to the nearest integer, then clamping it to the
    implementation-dependent maximum non-antialiased line width."

and suggested that when ES removed antialiased lines, they removed
"non-antialised" from that paragraph but probably should not have.

Going by that note, this patch restricts the quantization implemented in
fe74fee8fa721a only to regular aliased lines. This seems to keep the
tests fixed with that commit passing while fixing the broken test.

v2:
  - Drop one of the clamps (Ken, Marius)
  - Add a rule to prevent advertising line widths that when rounded go beyond
    the limits allowed by the hardware (Ken)
  - Update comments in the code accordingly (Ian)
  - Put the code in a utility function (Ian)

Fixes:
dEQP-GLES3.functional.rasterization.fbo.rbo_multisample_max.primitives.lines_wide

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90749
---
 src/mesa/drivers/dri/i965/brw_context.c   |  7 +++++++
 src/mesa/drivers/dri/i965/brw_util.h      | 15 +++++++++++++++
 src/mesa/drivers/dri/i965/gen6_sf_state.c |  6 +-----
 src/mesa/drivers/dri/i965/gen7_sf_state.c |  6 +-----
 src/mesa/drivers/dri/i965/gen8_sf_state.c |  6 +-----
 5 files changed, 25 insertions(+), 15 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_context.c b/src/mesa/drivers/dri/i965/brw_context.c
index 274a237..1e9ada2 100644
--- a/src/mesa/drivers/dri/i965/brw_context.c
+++ b/src/mesa/drivers/dri/i965/brw_context.c
@@ -442,6 +442,13 @@ brw_initialize_context_constants(struct brw_context *brw)
       ctx->Const.LineWidthGranularity = 0.5;
    }
 
+   /* For non-antialiased lines, we have to round the line width to the
+    * nearest whole number. Make sure that we don't advertise a line
+    * width that, when rounded, will be beyond the actual hardware
+    * maximum.
+    */
+   assert(roundf(ctx->Const.MaxLineWidth) <= ctx->Const.MaxLineWidth);
+
    ctx->Const.MinPointSize = 1.0;
    ctx->Const.MinPointSizeAA = 1.0;
    ctx->Const.MaxPointSize = 255.0;
diff --git a/src/mesa/drivers/dri/i965/brw_util.h b/src/mesa/drivers/dri/i965/brw_util.h
index b548d23..671d72e 100644
--- a/src/mesa/drivers/dri/i965/brw_util.h
+++ b/src/mesa/drivers/dri/i965/brw_util.h
@@ -35,9 +35,24 @@
 
 #include "main/mtypes.h"
 #include "main/imports.h"
+#include "brw_context.h"
 
 extern GLuint brw_translate_blend_factor( GLenum factor );
 extern GLuint brw_translate_blend_equation( GLenum mode );
 extern GLenum brw_fix_xRGB_alpha(GLenum function);
 
+static inline float
+brw_get_line_width(struct brw_context *brw)
+{
+   /* From the OpenGL 4.4 spec:
+    *
+    * "The actual width of non-antialiased lines is determined by rounding
+    * the supplied width to the nearest integer, then clamping it to the
+    * implementation-dependent maximum non-antialiased line width."
+    */
+   return CLAMP(!brw->ctx.Multisample._Enabled && !brw->ctx.Line.SmoothFlag
+                ? roundf(brw->ctx.Line.Width) : brw->ctx.Line.Width,
+                0.0, brw->ctx.Const.MaxLineWidth);
+}
+
 #endif
diff --git a/src/mesa/drivers/dri/i965/gen6_sf_state.c b/src/mesa/drivers/dri/i965/gen6_sf_state.c
index e445ce2..d577764 100644
--- a/src/mesa/drivers/dri/i965/gen6_sf_state.c
+++ b/src/mesa/drivers/dri/i965/gen6_sf_state.c
@@ -361,11 +361,7 @@ upload_sf_state(struct brw_context *brw)
 
    /* _NEW_LINE */
    {
-      /* OpenGL dictates that line width should be rounded to the nearest
-       * integer
-       */
-      float line_width =
-         roundf(CLAMP(ctx->Line.Width, 0.0, ctx->Const.MaxLineWidth));
+      float line_width = brw_get_line_width(brw);
       uint32_t line_width_u3_7 = U_FIXED(line_width, 7);
 
       /* Line width of 0 is not allowed when MSAA enabled */
diff --git a/src/mesa/drivers/dri/i965/gen7_sf_state.c b/src/mesa/drivers/dri/i965/gen7_sf_state.c
index 58e3337..87ff284 100644
--- a/src/mesa/drivers/dri/i965/gen7_sf_state.c
+++ b/src/mesa/drivers/dri/i965/gen7_sf_state.c
@@ -192,11 +192,7 @@ upload_sf_state(struct brw_context *brw)
 
    /* _NEW_LINE */
    {
-      /* OpenGL dictates that line width should be rounded to the nearest
-       * integer
-       */
-      float line_width =
-         roundf(CLAMP(ctx->Line.Width, 0.0, ctx->Const.MaxLineWidth));
+      float line_width = brw_get_line_width(brw);
       uint32_t line_width_u3_7 = U_FIXED(line_width, 7);
       /* Line width of 0 is not allowed when MSAA enabled */
       if (ctx->Multisample._Enabled) {
diff --git a/src/mesa/drivers/dri/i965/gen8_sf_state.c b/src/mesa/drivers/dri/i965/gen8_sf_state.c
index 52a21b6..83ef62b 100644
--- a/src/mesa/drivers/dri/i965/gen8_sf_state.c
+++ b/src/mesa/drivers/dri/i965/gen8_sf_state.c
@@ -154,11 +154,7 @@ upload_sf(struct brw_context *brw)
        dw1 |= GEN6_SF_VIEWPORT_TRANSFORM_ENABLE;
 
    /* _NEW_LINE */
-   /* OpenGL dictates that line width should be rounded to the nearest
-    * integer
-    */
-   float line_width =
-      roundf(CLAMP(ctx->Line.Width, 0.0, ctx->Const.MaxLineWidth));
+   float line_width = brw_get_line_width(brw);
    uint32_t line_width_u3_7 = U_FIXED(line_width, 7);
    if (line_width_u3_7 == 0)
       line_width_u3_7 = 1;
-- 
2.1.0