Mesa (main): panvk: Conform viewport code to Vulkan spec

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Module: Mesa
Branch: main
Commit: 0bd9e4d3b60ce8a87624fb3562a5ffde2345d868
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=0bd9e4d3b60ce8a87624fb3562a5ffde2345d868

Author: Alyssa Rosenzweig <alyssa at collabora.com>
Date:   Mon Apr 25 11:32:39 2022 -0400

panvk: Conform viewport code to Vulkan spec

The depth equations weren't quite right, with spec citations to prove it. This
didn't fix the test I was debugging, but it surely fixed /something/.

Signed-off-by: Alyssa Rosenzweig <alyssa at collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16155>

---

 src/panfrost/vulkan/panvk_cs.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/panfrost/vulkan/panvk_cs.c b/src/panfrost/vulkan/panvk_cs.c
index cf1915b9287..fe717dd9ae2 100644
--- a/src/panfrost/vulkan/panvk_cs.c
+++ b/src/panfrost/vulkan/panvk_cs.c
@@ -30,20 +30,38 @@
 #include "panvk_cs.h"
 #include "panvk_private.h"
 
+/*
+ * Upload the viewport scale. Defined as (px/2, py/2, pz) at the start of section
+ * 24.5 ("Controlling the Viewport") of the Vulkan spec. At the end of the
+ * section, the spec defines:
+ *
+ * px = width
+ * py = height
+ * pz = maxDepth - minDepth
+ */
 void
 panvk_sysval_upload_viewport_scale(const VkViewport *viewport,
                                    union panvk_sysval_data *data)
 {
    data->f32[0] = 0.5f * viewport->width;
    data->f32[1] = 0.5f * viewport->height;
-   data->f32[2] = 0.5f * (viewport->maxDepth - viewport->minDepth);
+   data->f32[2] = (viewport->maxDepth - viewport->minDepth);
 }
 
+/*
+ * Upload the viewport offset. Defined as (ox, oy, oz) at the start of section
+ * 24.5 ("Controlling the Viewport") of the Vulkan spec. At the end of the
+ * section, the spec defines:
+ *
+ * ox = x + width/2
+ * oy = y + height/2
+ * oz = minDepth
+ */
 void
 panvk_sysval_upload_viewport_offset(const VkViewport *viewport,
                                     union panvk_sysval_data *data)
 {
    data->f32[0] = (0.5f * viewport->width) + viewport->x;
    data->f32[1] = (0.5f * viewport->height) + viewport->y;
-   data->f32[2] = (0.5f * (viewport->maxDepth - viewport->minDepth)) + viewport->minDepth;
+   data->f32[2] = viewport->minDepth;
 }