From a85b62fdb2e153195a52cef8ecad27432bf37f50 Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Wed, 21 Jun 2023 08:43:54 -0700
Subject: Flip y-coordinate in view-texture shader and use texelFetch to avoid
 bilinear sampling.

---
 gfx/shaders/view_texture.frag | 8 ++++++--
 gfx/shaders/view_texture.vert | 8 ++++++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/gfx/shaders/view_texture.frag b/gfx/shaders/view_texture.frag
index a81263b..f01127d 100644
--- a/gfx/shaders/view_texture.frag
+++ b/gfx/shaders/view_texture.frag
@@ -6,6 +6,10 @@ layout (location = 0) out vec4 Colour;
 
 void main()
 {
-  vec3 colour = texture(Texture, Texcoord).rgb;
-  Colour = vec4(pow(colour, vec3(1.0 / 2.2)), 1.0);
+    // My OpenGL driver seems to be ignoring GL_NEAREST for
+    // GL_TEXTURE_MAG_FILTER and still applies bilinear sampling. Use texelFetch
+    // instead of texture() instead.
+    ivec2 st = ivec2(Texcoord * vec2(textureSize(Texture, 0)));
+    vec3 colour = texelFetch(Texture, st, 0).rgb;
+    Colour = vec4(pow(colour, vec3(1.0 / 2.2)), 1.0);
 }
diff --git a/gfx/shaders/view_texture.vert b/gfx/shaders/view_texture.vert
index 49a0422..4e3c7d7 100644
--- a/gfx/shaders/view_texture.vert
+++ b/gfx/shaders/view_texture.vert
@@ -4,6 +4,10 @@ out vec2 Texcoord;
 
 void main()
 {
-  Texcoord = Position * vec2(0.5) + vec2(0.5);  // Map from [-1, +1] to [0, 1].
-  gl_Position = vec4(Position, 0.0, 1.0);
+    Texcoord = Position * vec2(0.5) + vec2(0.5);// Map from [-1, +1] to [0, 1].
+    // The Gfx library is written to work with the glTF sample models, which
+    // seem to want the textures loaded "as is" without flipping. Flip the
+    // y-coordinate here so that the texture appears as expected.
+    Texcoord.y = 1.0 - Texcoord.y;
+    gl_Position = vec4(Position, 0.0, 1.0);
 }
-- 
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