Relativistic crumbling

- Apply crumbling texture based on model space coordinates, not world
  space.
- Discard based both on crumbling alpha and diffuse alpha.

src/main/java/com/jozufozu/flywheel/backend/engine/instancing/InstancingEngine.java

@@ -94,11 +94,24 @@ public class InstancingEngine extends AbstractEngine {
 		}
 
 		try (var state = GlStateTracker.getRestoreState()) {
-			ModelBakery.DESTROY_TYPES.get(progress)
-					.setupRenderState();
+			var crumblingType = ModelBakery.DESTROY_TYPES.get(progress);
 
 			for (var entry : drawMap.entrySet()) {
-				setup(entry.getKey(), Contexts.CRUMBLING);
+				var shader = entry.getKey();
+
+				setup(shader, Contexts.CRUMBLING);
+
+				shader.material().setup();
+
+				int renderTex = RenderSystem.getShaderTexture(0);
+
+				shader.material().clear();
+
+				crumblingType.setupRenderState();
+
+				RenderSystem.setShaderTexture(1, renderTex);
+				GlTextureUnit.T1.makeActive();
+				RenderSystem.bindTexture(renderTex);
 
 				for (Runnable draw : entry.getValue()) {
 					draw.run();

src/main/java/com/jozufozu/flywheel/lib/context/Contexts.java

@@ -17,10 +17,10 @@ public final class Contexts {
 		GlProgram.unbind();
 	}));
 
-	// TODO: can we make crumbling a fragment material?
-	public static final SimpleContext CRUMBLING = Context.REGISTRY.registerAndGet(new SimpleContext(Files.WORLD_VERTEX, Files.CRUMBLING_FRAGMENT, program -> {
+	public static final SimpleContext CRUMBLING = Context.REGISTRY.registerAndGet(new SimpleContext(Files.CRUMBLING_VERTEX, Files.CRUMBLING_FRAGMENT, program -> {
 		program.bind();
-		program.setSamplerBinding("flw_diffuseTex", 0);
+		program.setSamplerBinding("flw_crumblingTex", 0);
+		program.setSamplerBinding("flw_diffuseTex", 1);
 		GlProgram.unbind();
 	}));
 

src/main/resources/assets/flywheel/flywheel/context/common.vert

@@ -1,8 +0,0 @@
-#include "flywheel:api/vertex.glsl"
-#include "flywheel:util/fog.glsl"
-
-void flw_contextVertex() {
-    flw_distance = fog_distance(flw_vertexPos.xyz, flywheel.cameraPos.xyz, flywheel.fogShape);
-    gl_Position = flywheel.viewProjection * flw_vertexPos;
-    flw_vertexNormal = normalize(flw_vertexNormal);
-}

src/main/resources/assets/flywheel/flywheel/context/crumbling.frag

@@ -1,32 +1,27 @@
 #include "flywheel:api/fragment.glsl"
 
+// optimize discard usage
+#ifdef ALPHA_DISCARD
+#ifdef GL_ARB_conservative_depth
+layout (depth_greater) out float gl_FragDepth;
+#endif
+#endif
+
 uniform sampler2D flw_diffuseTex;
+uniform sampler2D flw_crumblingTex;
+
+in vec2 flw_crumblingTexCoord;
 
 out vec4 fragColor;
 
-vec2 flattenedPos(vec3 pos, vec3 normal) {
-    pos -= floor(pos) + vec3(0.5);
-
-    float sinYRot = -normal.x;
-    vec2 XZ = normal.xz;
-    float sqLength = dot(XZ, XZ);
-    if (sqLength > 0) {
-        sinYRot *= inversesqrt(sqLength);
-        sinYRot = clamp(sinYRot, -1, 1);
-    }
-
-    vec3 tangent = vec3(sqrt(1 - sinYRot * sinYRot) * (normal.z < 0 ? -1 : 1), 0, sinYRot);
-    vec3 bitangent = cross(tangent, normal);
-    mat3 tbn = mat3(tangent, bitangent, normal);
-
-    // transpose is the same as inverse for orthonormal matrices
-    return (transpose(tbn) * pos).xy + vec2(0.5);
-}
+vec4 flw_crumblingSampleColor;
 
 void flw_initFragment() {
-    flw_sampleColor = texture(flw_diffuseTex, flattenedPos(flw_vertexPos.xyz, flw_vertexNormal));
-    // Crumbling ignores vertex colors
-    flw_fragColor = flw_sampleColor;
+    flw_crumblingSampleColor = texture(flw_crumblingTex, flw_crumblingTexCoord);
+    flw_sampleColor = texture(flw_diffuseTex, flw_vertexTexCoord);
+
+    // Let the other components modify the diffuse color as they normally would.
+    flw_fragColor = flw_vertexColor * flw_sampleColor;
     flw_fragOverlay = flw_vertexOverlay;
     flw_fragLight = flw_vertexLight;
 }
@@ -34,10 +29,10 @@ void flw_initFragment() {
 void flw_contextFragment() {
     vec4 color = flw_fragColor;
 
-    // Ignore the discard predicate since we control the texture.
-    if (color.a < 0.01) {
+    // Still need to discard based on the diffuse color so we don't crumble over empty space.
+    if (flw_discardPredicate(color) || flw_crumblingSampleColor.a < 0.01) {
         discard;
     }
 
-    fragColor = flw_fogFilter(color);
+    fragColor = flw_fogFilter(flw_crumblingSampleColor);
 }

src/main/resources/assets/flywheel/flywheel/context/crumbling.vert

@@ -1 +1,37 @@
-#include "flywheel:context/common.vert"
+#include "flywheel:api/vertex.glsl"
+#include "flywheel:util/fog.glsl"
+
+out vec2 flw_crumblingTexCoord;
+
+vec3 tangent(vec3 normal) {
+    float sinYRot = -normal.x;
+    vec2 XZ = normal.xz;
+    float sqLength = dot(XZ, XZ);
+    if (sqLength > 0) {
+        sinYRot *= inversesqrt(sqLength);
+        sinYRot = clamp(sinYRot, -1, 1);
+    }
+
+    return vec3(sqrt(1 - sinYRot * sinYRot) * (normal.z < 0 ? -1 : 1), 0, sinYRot);
+}
+
+vec2 flattenedPos(vec3 pos, vec3 normal) {
+    pos -= vec3(0.5);
+
+    vec3 tangent = tangent(normal);
+    vec3 bitangent = cross(tangent, normal);
+    mat3 tbn = mat3(tangent, bitangent, normal);
+
+    // transpose is the same as inverse for orthonormal matrices
+    return (transpose(tbn) * pos).xy + vec2(0.5);
+}
+
+void flw_initVertex() {
+    flw_crumblingTexCoord = flattenedPos(flw_vertexPos.xyz, flw_vertexNormal);
+}
+
+void flw_contextVertex() {
+    flw_distance = fog_distance(flw_vertexPos.xyz, flywheel.cameraPos.xyz, flywheel.fogShape);
+    gl_Position = flywheel.viewProjection * flw_vertexPos;
+    flw_vertexNormal = normalize(flw_vertexNormal);
+}

src/main/resources/assets/flywheel/flywheel/context/world.vert

@@ -1 +1,12 @@
-#include "flywheel:context/common.vert"
+#include "flywheel:api/vertex.glsl"
+#include "flywheel:util/fog.glsl"
+
+void flw_initVertex() {
+    // noop
+}
+
+void flw_contextVertex() {
+    flw_distance = fog_distance(flw_vertexPos.xyz, flywheel.cameraPos.xyz, flywheel.fogShape);
+    gl_Position = flywheel.viewProjection * flw_vertexPos;
+    flw_vertexNormal = normalize(flw_vertexNormal);
+}

src/main/resources/assets/flywheel/flywheel/internal/indirect_draw.vert

@@ -26,6 +26,7 @@ void main() {
     _flw_materialFragmentID = drawCommands[batchID].fragmentMaterialID;
 
     flw_layoutVertex();
+    flw_initVertex();
     flw_instanceVertex(i);
     flw_materialVertex();
     flw_contextVertex();

src/main/resources/assets/flywheel/flywheel/internal/instanced_arrays_draw.vert

@@ -9,6 +9,7 @@ void main() {
     FlwInstance i = _flw_unpackInstance();
 
     flw_layoutVertex();
+    flw_initVertex();
     flw_instanceVertex(i);
     flw_materialVertex();
     flw_contextVertex();