Who's counting?

- Atomically count instances in indirect instancer
- Fixes indirect draws/instancers never being deleted
- Fix baseDraw being set incorrectly on intel
- Handle setting baseDraw in GlCompat#safeMultiDrawElementsIndirect

common/src/backend/java/dev/engine_room/flywheel/backend/engine/indirect/IndirectCullingGroup.java

@@ -199,7 +199,6 @@ public void submit(VisualType visualType) {
 		drawBarrier();
 
 		GlProgram lastProgram = null;
-		int baseDrawUniformLoc = -1;
 
 		for (var multiDraw : multiDraws.get(visualType)) {
 			var drawProgram = programs.getIndirectProgram(instanceType, multiDraw.embedded ? ContextShader.EMBEDDED : ContextShader.DEFAULT, multiDraw.material);
@@ -208,14 +207,11 @@ public void submit(VisualType visualType) {
 
 				// Don't need to do this unless the program changes.
 				drawProgram.bind();
-				baseDrawUniformLoc = drawProgram.getUniformLocation("_flw_baseDraw");
 			}
 
-			glUniform1ui(baseDrawUniformLoc, multiDraw.start);
-
 			MaterialRenderState.setup(multiDraw.material);
 
-			multiDraw.submit();
+			multiDraw.submit(drawProgram);
 		}
 	}
 
@@ -290,8 +286,8 @@ public boolean checkEmptyAndDelete() {
 	}
 
 	private record MultiDraw(Material material, boolean embedded, int start, int end) {
-		private void submit() {
-			GlCompat.safeMultiDrawElementsIndirect(GL_TRIANGLES, GL_UNSIGNED_INT, this.start * IndirectBuffers.DRAW_COMMAND_STRIDE, this.end - this.start, (int) IndirectBuffers.DRAW_COMMAND_STRIDE);
+		private void submit(GlProgram drawProgram) {
+			GlCompat.safeMultiDrawElementsIndirect(drawProgram, GL_TRIANGLES, GL_UNSIGNED_INT, this.start, this.end, IndirectBuffers.DRAW_COMMAND_STRIDE);
 		}
 	}
 }

common/src/backend/java/dev/engine_room/flywheel/backend/engine/indirect/IndirectInstancer.java

@@ -25,6 +25,9 @@ public class IndirectInstancer<I extends Instance> extends AbstractInstancer<I>
 	private final Vector4fc boundingSphere;
 
 	private final AtomicReference<InstancePage<I>[]> pages = new AtomicReference<>(pageArray(0));
+
+	private final AtomicInteger instanceCount = new AtomicInteger(0);
+
 	/**
 	 * The set of pages whose count changed and thus need their descriptor re-uploaded.
 	 */
@@ -145,6 +148,8 @@ public boolean add(I instance, InstanceHandleImpl<I> handle) {
 						// We just filled the 17th instance, so we are no longer mergeable.
 						parent.mergeablePages.clear(pageNo);
 					}
+
+					parent.instanceCount.incrementAndGet();
 					return true;
 				}
 			}
@@ -203,6 +208,7 @@ private void clear(int localIndex) {
 					}
 					// Set full page last so that other threads don't race to set the other bitsets.
 					parent.fullPages.clear(pageNo);
+					parent.instanceCount.decrementAndGet();
 					break;
 				}
 			}
@@ -538,9 +544,7 @@ private void addInner(I instance, InstanceHandleImpl<I> handle) {
 	}
 
 	public int instanceCount() {
-		// Not exactly accurate but it's an upper bound.
-		// TODO: maybe this could be tracked with an AtomicInteger?
-		return pages.get().length << ObjectStorage.LOG_2_PAGE_SIZE;
+		return instanceCount.get();
 	}
 
 	/**

common/src/backend/java/dev/engine_room/flywheel/backend/gl/GlCompat.java

@@ -16,6 +16,7 @@
 
 import dev.engine_room.flywheel.backend.FlwBackend;
 import dev.engine_room.flywheel.backend.compile.core.Compilation;
+import dev.engine_room.flywheel.backend.gl.shader.GlProgram;
 import dev.engine_room.flywheel.backend.glsl.GlslVersion;
 import dev.engine_room.flywheel.lib.math.MoreMath;
 
@@ -78,15 +79,20 @@ public static void safeShaderSource(int glId, CharSequence source) {
 	 * but uses consecutive DI instead of MDI if MDI is known to not work well with the current driver.
 	 * Unlike the original function, stride cannot be equal to 0.
 	 */
-	public static void safeMultiDrawElementsIndirect(int mode, int type, long indirect, int drawcount, int stride) {
+	public static void safeMultiDrawElementsIndirect(GlProgram drawProgram, int mode, int type, int start, int end, long stride) {
+		var count = end - start;
+		long indirect = start * stride;
+
 		if (GlCompat.DRIVER == Driver.INTEL) {
-			// Intel renders garbage with MDI, but consecutive DI works fine.
-			for (int i = 0; i < drawcount; i++) {
+			// Intel renders garbage with MDI, but consecutive DI works "fine".
+			for (int i = 0; i < count; i++) {
+				drawProgram.setUInt("_flw_baseDraw", start + i);
 				GL40.glDrawElementsIndirect(mode, type, indirect);
 				indirect += stride;
 			}
 		} else {
-			GL43.glMultiDrawElementsIndirect(mode, type, indirect, drawcount, stride);
+			drawProgram.setUInt("_flw_baseDraw", start);
+			GL43.glMultiDrawElementsIndirect(mode, type, indirect, count, (int) stride);
 		}
 	}