Draw glass on every version

1.21.6 to 1.21.10 draw glass as 1.21.11 does, without samplers, and the
glass shader imports vanilla's transforms block, whose layout differs
between them. 1.21.4 and 1.21.5 draw straight into the framebuffer,
so the game is saved before the screen blurs it, and glass is a render
layer: with a pipeline on 1.21.5 and a shader program on 1.21.4.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/main/resources/assets/saturnclient/shaders/core/glass.fsh

@@ -1,13 +1,10 @@
 #version 330
 
-// Saturn's glass: the blurred game behind the screen, cut to a panel's shape.
+// Saturn's glass: the blurred game behind the screen, cut to a panel's shape. For 1.21.6 and
+// later; glass_pre_1_21_6.fsh (with glass.json, the program 1.21.4 loads) is for older versions.
 
-layout(std140) uniform DynamicTransforms {
-    mat4 ModelViewMat;
-    vec4 ColorModulator;
-    vec3 ModelOffset;
-    mat4 TextureMat;
-};
+// Vanilla's own, since its layout changes between versions (1.21.11 dropped LineWidth)
+#moj_import <minecraft:dynamictransforms.glsl>
 
 // The panel's rounded rectangle, the same texture its background is drawn with
 uniform sampler2D Sampler0;

src/main/resources/assets/saturnclient/shaders/core/glass.json

@@ -0,0 +1,13 @@
+{
+    "vertex": "minecraft:core/position_tex_color",
+    "fragment": "saturnclient:core/glass_pre_1_21_6",
+    "samplers": [
+        { "name": "Sampler0" },
+        { "name": "Sampler1" }
+    ],
+    "uniforms": [
+        { "name": "ModelViewMat", "type": "matrix4x4", "count": 16, "values": [ 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0 ] },
+        { "name": "ProjMat", "type": "matrix4x4", "count": 16, "values": [ 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 1.0 ] },
+        { "name": "ColorModulator", "type": "float", "count": 4, "values": [ 1.0, 1.0, 1.0, 1.0 ] }
+    ]
+}

src/main/resources/assets/saturnclient/shaders/core/glass_pre_1_21_6.fsh

@@ -0,0 +1,27 @@
+#version 150
+
+// Saturn's glass (see glass.fsh), for 1.21.4 and 1.21.5, which set uniforms one by one instead of in
+// blocks.
+
+uniform vec4 ColorModulator;
+
+// The panel's rounded rectangle, the same texture its background is drawn with
+uniform sampler2D Sampler0;
+// The game behind the screen, blurred, the size of the framebuffer
+uniform sampler2D Sampler1;
+
+in vec2 texCoord0;
+in vec4 vertexColor;
+
+out vec4 fragColor;
+
+void main() {
+    float mask = texture(Sampler0, texCoord0).a * vertexColor.a;
+    if (mask == 0.0) {
+        discard;
+    }
+
+    // The blurred copy lines up with the framebuffer being drawn to.
+    vec2 screenUv = gl_FragCoord.xy / vec2(textureSize(Sampler1, 0));
+    fragColor = vec4(texture(Sampler1, screenUv).rgb, mask) * ColorModulator;
+}