gpu: reverse z

This changes the projection to (in row-major order):

2/w      0     0      0
0     -2/h     0      0
0        0     0     2n
0        0     1      0

Which changes the z calculation from (z-100)/z to 100/z.

runelite-client/src/main/java/net/runelite/client/plugins/gpu/Mat4.java

@@ -98,8 +98,8 @@ public static float[] projection(float w, float h, float n)
 			{
 				2 / w, 0, 0, 0,
 				0, -2 / h, 0, 0,
-				0, 0, 1, 1,
-				0, 0, -2 * n, 0
+				0, 0, 0, 1,
+				0, 0, 2 * n, 0
 			};
 	}
 

runelite-client/src/main/resources/net/runelite/client/plugins/gpu/frag.glsl

@@ -24,7 +24,8 @@
  */
 #version 330
 
-//#define FRAG_UVS
+#define FRAG_UVS
+//#define ZBUF
 
 uniform sampler2DArray textures;
 uniform float brightness;
@@ -38,12 +39,23 @@ noperspective centroid in float fHsl;
 flat in int fTextureId;
 in vec2 fUv;
 in float fFogAmount;
+#ifdef ZBUF
+in float fDepth;
+#endif
 
 out vec4 FragColor;
 
 #include "hsl_to_rgb.glsl"
 #include "colorblind.glsl"
 
+#ifdef ZBUF
+float linear_depth(float depth) {
+  // depth is computed as 100/z, solve for z
+  float z = 100 / depth;
+  return 1 - z / 10000;  // we don't have a far plane, but the client uses 10000
+}
+#endif
+
 void main() {
   vec4 c;
 
@@ -68,13 +80,24 @@ void main() {
   }
 
   vec3 mixedColor = mix(c.rgb, fogColor.rgb, fFogAmount);
+  FragColor = vec4(mixedColor, c.a);
+
 #ifdef FRAG_UVS
   if (fTextureId > 0) {
     FragColor = vec4(fUv.x, 0, fUv.y, 1);
-  } else {
+  }
 #endif
-    FragColor = vec4(mixedColor, c.a);
-#ifdef FRAG_UVS
+
+#ifdef ZBUF
+  float dc = linear_depth(fDepth);
+  if (dc > 1.0) {
+    FragColor = vec4(1, 0, 0, 1);
+  } else if (dc < -1.0) {
+    FragColor = vec4(0, 0, 1, 1);
+  } else if (dc < 0.0) {
+    FragColor = vec4(0, 1, 0, 1);
+  } else {
+    FragColor = vec4(dc, dc, dc, 1);
   }
 #endif
 }

runelite-client/src/main/resources/net/runelite/client/plugins/gpu/geom.glsl

@@ -25,6 +25,8 @@
 
 #version 330
 
+//#define ZBUF
+
 // smallest unit of the texture which can be moved per tick. textures are all
 // 128x128px - so this is equivalent to +1px
 #define TEXTURE_ANIM_UNIT (1.0f / 128.0f)
@@ -62,6 +64,9 @@ noperspective centroid out float fHsl;
 flat out int fTextureId;
 out vec2 fUv;
 out float fFogAmount;
+#ifdef ZBUF
+out float fDepth;
+#endif
 
 void main() {
   int textureId = gTextureId[0];
@@ -87,7 +92,13 @@ void main() {
     fTextureId = gTextureId[i];
     fUv = uv[i];
     fFogAmount = gFogAmount[i];
-    gl_Position = projectionMatrix * vec4(gVertex[i], 1);
+
+    vec4 pos = projectionMatrix * vec4(gVertex[i], 1);
+#ifdef ZBUF
+    fDepth = pos.z / pos.w;
+#endif
+    gl_Position = pos;
+
     EmitVertex();
   }