From 4292304df18baf31a7d3c78a1f1306979783c8ce Mon Sep 17 00:00:00 2001
From: Luke Benstead <kazade@gmail.com>
Date: Tue, 24 Mar 2020 13:58:44 +0000
Subject: [PATCH] Implement glClearDepth

---
 GL/draw.c  | 11 ++++++++---
 GL/state.c |  8 ++++----
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/GL/draw.c b/GL/draw.c
index d8217c8..79a00ff 100644
--- a/GL/draw.c
+++ b/GL/draw.c
@@ -1171,10 +1171,15 @@ GL_FORCE_INLINE void divide(SubmissionTarget* target) {
         float f = MATH_fsrra(vertex->w * vertex->w);
         vertex->xyz[0] *= f;
         vertex->xyz[1] *= f;
+        vertex->xyz[2] = f;
 
-        /* Scale depending on glDepthRange */
-        vertex->xyz[2] = 1.0f - ((DEPTH_RANGE_MULTIPLIER_L * vertex->xyz[2] * f) + DEPTH_RANGE_MULTIPLIER_H);
-
+        /* FIXME: Consider taking glDepthRange into account. PVR is designed to use invW rather
+         * than Z which is unlike most GPUs - this apparently provides advantages.
+         *
+         * This can be done (if Z is between -1 and 1) with:
+         *
+         * //((DEPTH_RANGE_MULTIPLIER_L * vertex->xyz[2] * f) + DEPTH_RANGE_MULTIPLIER_H);
+         */
         ++vertex;
     }
 }
diff --git a/GL/state.c b/GL/state.c
index 72a54e2..a705526 100644
--- a/GL/state.c
+++ b/GL/state.c
@@ -274,6 +274,7 @@ void _glInitContext() {
     GL_CONTEXT.fmt.uv = PVR_UVFMT_32BIT;
     GL_CONTEXT.gen.color_clamp = PVR_CLRCLAMP_DISABLE;
 
+    glClearDepth(1.0f);
     glDepthFunc(GL_LESS);
     glDepthMask(GL_TRUE);
     glFrontFace(GL_CCW);
@@ -439,13 +440,12 @@ GLAPI void APIENTRY glClearColor(GLfloat r, GLfloat g, GLfloat b, GLfloat a) {
 
 /* Depth Testing */
 GLAPI void APIENTRY glClearDepthf(GLfloat depth) {
-    _GL_UNUSED(depth);
-
+    glClearDepth(depth);
 }
 
 GLAPI void APIENTRY glClearDepth(GLfloat depth) {
-    _GL_UNUSED(depth);
-
+    /* We reverse because using invW means that farther Z == lower number */
+    pvr_set_zclip(1.0f - depth);
 }
 
 GLAPI void APIENTRY glDrawBuffer(GLenum mode) {