Squashed commit of the following:

commit b2ffbe1
Author: coderbot <coderbot16@gmail.com>
Date:   Tue Mar 23 12:40:08 2021 -0700

    Fix the placeholder normal map texture having incorrect content

commit 306b490
Author: coderbot <coderbot16@gmail.com>
Date:   Tue Mar 23 12:05:14 2021 -0700

    Add placeholder PBR textures fixing many issues with many shaderpacks (IrisShaders#130)

commit 503952c
Author: coderbot <coderbot16@gmail.com>
Date:   Tue Mar 23 10:05:28 2021 -0700

    Fix ArrayIndexOutOfBoundsException when parsing buffer clear directives

src/main/java/net/coderbot/iris/pipeline/DeferredWorldRenderingPipeline.java

@@ -12,6 +12,7 @@
 import net.coderbot.iris.layer.GbufferProgram;
 import net.coderbot.iris.postprocess.CompositeRenderer;
 import net.coderbot.iris.rendertarget.BuiltinNoiseTexture;
+import net.coderbot.iris.rendertarget.SingleColorTexture;
 import net.coderbot.iris.rendertarget.RenderTargets;
 import net.coderbot.iris.shaderpack.ProgramSet;
 import net.coderbot.iris.shaderpack.ProgramSource;
@@ -73,6 +74,8 @@ public class DeferredWorldRenderingPipeline implements WorldRenderingPipeline {
 
 	private final EmptyShadowMapRenderer shadowMapRenderer;
 	private final CompositeRenderer compositeRenderer;
+	private final SingleColorTexture normals;
+	private final SingleColorTexture specular;
 
 	private final int waterId;
 
@@ -108,6 +111,25 @@ public DeferredWorldRenderingPipeline(ProgramSet programs) {
 		this.clearMainBuffers = renderTargets.createFramebufferWritingToMain(buffersToBeCleared);
 		this.baseline = renderTargets.createFramebufferWritingToMain(new int[] {0});
 
+		// Don't clobber anything in texture unit 0. It probably won't cause issues, but we're just being cautious here.
+		GlStateManager.activeTexture(GL20C.GL_TEXTURE2);
+
+		// Ensure that the pixel storage mode is in a sane state, otherwise the uploaded texture data will be quite
+		// incorrect.
+		//
+		// It is likely that this also avoids the crashes on AMD that I previously experienced with texture creation.
+		//
+		// This code is from Canvas: https://github.com/grondag/canvas/commit/f0ab652d7a8b7cc9febf0209bee15cffce9eac83
+		GlStateManager.pixelStore(GL20C.GL_UNPACK_ROW_LENGTH, 0);
+		GlStateManager.pixelStore(GL20C.GL_UNPACK_SKIP_ROWS, 0);
+		GlStateManager.pixelStore(GL20C.GL_UNPACK_SKIP_PIXELS, 0);
+		GlStateManager.pixelStore(GL20C.GL_UNPACK_ALIGNMENT, 4);
+
+		// Create some placeholder PBR textures for now
+		normals = new SingleColorTexture(127, 127, 255, 255);
+		specular = new SingleColorTexture(0, 0, 0, 0);
+		GlStateManager.activeTexture(GL20C.GL_TEXTURE0);
+
 		this.shadowMapRenderer = new EmptyShadowMapRenderer(2048);
 		this.compositeRenderer = new CompositeRenderer(programs, renderTargets, shadowMapRenderer);
 	}
@@ -337,6 +359,10 @@ public void use() {
 			// a given program and bind the required textures instead.
 			GlStateManager.activeTexture(GL15C.GL_TEXTURE15);
 			BuiltinNoiseTexture.bind();
+			GlStateManager.activeTexture(GL15C.GL_TEXTURE2);
+			GlStateManager.bindTexture(normals.getTextureId());
+			GlStateManager.activeTexture(GL15C.GL_TEXTURE3);
+			GlStateManager.bindTexture(specular.getTextureId());
 			GlStateManager.activeTexture(GL15C.GL_TEXTURE4);
 			GlStateManager.bindTexture(shadowMapRenderer.getDepthTextureId());
 			GlStateManager.activeTexture(GL15C.GL_TEXTURE5);

src/main/java/net/coderbot/iris/rendertarget/SingleColorTexture.java

@@ -0,0 +1,40 @@
+package net.coderbot.iris.rendertarget;
+
+import com.mojang.blaze3d.platform.GlStateManager;
+import net.coderbot.iris.gl.GlResource;
+import org.lwjgl.BufferUtils;
+import org.lwjgl.opengl.GL11C;
+import org.lwjgl.opengl.GL13C;
+
+import java.nio.ByteBuffer;
+
+public class SingleColorTexture extends GlResource {
+	public SingleColorTexture(int red, int green, int blue, int alpha) {
+		super(GL11C.glGenTextures());
+		GlStateManager.bindTexture(getGlId());
+
+		ByteBuffer pixel = BufferUtils.createByteBuffer(4);
+		pixel.put((byte) red);
+		pixel.put((byte) green);
+		pixel.put((byte) blue);
+		pixel.put((byte) alpha);
+		pixel.position(0);
+
+		GL11C.glTexParameteri(GL11C.GL_TEXTURE_2D, GL11C.GL_TEXTURE_MIN_FILTER, GL11C.GL_LINEAR);
+		GL11C.glTexParameteri(GL11C.GL_TEXTURE_2D, GL11C.GL_TEXTURE_MAG_FILTER, GL11C.GL_LINEAR);
+		GL11C.glTexParameteri(GL11C.GL_TEXTURE_2D, GL11C.GL_TEXTURE_WRAP_S, GL13C.GL_REPEAT);
+		GL11C.glTexParameteri(GL11C.GL_TEXTURE_2D, GL11C.GL_TEXTURE_WRAP_T, GL13C.GL_REPEAT);
+		GL11C.glTexImage2D(GL11C.GL_TEXTURE_2D, 0, GL11C.GL_RGBA, 1, 1, 0, GL11C.GL_RGBA, GL11C.GL_UNSIGNED_BYTE, pixel);
+
+		GlStateManager.bindTexture(0);
+	}
+
+	public int getTextureId() {
+		return getGlId();
+	}
+
+	@Override
+	protected void destroyInternal() {
+		GL11C.glDeleteTextures(getGlId());
+	}
+}

src/main/java/net/coderbot/iris/shaderpack/PackDirectives.java

@@ -4,26 +4,32 @@
 import it.unimi.dsi.fastutil.ints.IntList;
 import net.coderbot.iris.Iris;
 import net.coderbot.iris.gl.texture.InternalTextureFormat;
+import net.coderbot.iris.rendertarget.RenderTargets;
 
 import java.util.Arrays;
 import java.util.OptionalInt;
 
 public class PackDirectives {
 	private InternalTextureFormat[] requestedTextureFormats;
-	private IntList buffersToBeCleared;
+	private boolean[] clearBuffers;
 
 	PackDirectives() {
-		requestedTextureFormats = new InternalTextureFormat[8];
+		requestedTextureFormats = new InternalTextureFormat[RenderTargets.MAX_RENDER_TARGETS];
 		Arrays.fill(requestedTextureFormats, InternalTextureFormat.RGBA);
 
-		// TODO: Don't assume that there are only 8 buffers
-		buffersToBeCleared = new IntArrayList(new int[]{0, 1, 2, 3, 4, 5, 6, 7});
+		clearBuffers = new boolean[RenderTargets.MAX_RENDER_TARGETS];
+		Arrays.fill(clearBuffers, true);
 	}
 
-	// TODO: These are currently hardcoded to work with Sildur's. They will need to be properly parsed from shaders.properties.
-	// Some of these values also come from individual shader files, such as the requested buffer formats.
-
 	public IntList getBuffersToBeCleared() {
+		IntList buffersToBeCleared = new IntArrayList();
+
+		for (int i = 0; i < clearBuffers.length; i++) {
+			if (clearBuffers[i]) {
+				buffersToBeCleared.add(i);
+			}
+		}
+
 		return buffersToBeCleared;
 	}
 
@@ -49,7 +55,9 @@ void accept(ConstDirectiveParser.ConstDirective directive) {
 		} else if (type == ConstDirectiveParser.Type.BOOL && key.endsWith("Clear") && value.equals("false")) {
 			String bufferName = key.substring(0, key.length() - "Clear".length());
 
-			bufferNameToIndex(bufferName).ifPresent(buffersToBeCleared::removeInt);
+			bufferNameToIndex(bufferName).ifPresent(index -> {
+				clearBuffers[index] = false;
+			});
 		}
 	}
 

src/main/java/net/coderbot/iris/texunits/TextureUnit.java

@@ -5,8 +5,8 @@
 public enum TextureUnit {
 	TERRAIN(0),
 	LIGHTMAP(1),
-	// TODO: Relocate this to a different texture unit, this is used by the normal map for normal shaders
-	OVERLAY(2);
+	// TODO: Relocate this to a different texture unit, this is used by depthtex0...
+	OVERLAY(6);
 
 	private final int samplerId;
 	private final int unitId;

src/main/java/net/coderbot/iris/uniforms/CommonUniforms.java

@@ -52,6 +52,8 @@ public static void addCommonUniforms(UniformHolder uniforms, IdMap idMap) {
 			.uniform1i(ONCE, "lightmap", TextureUnit.LIGHTMAP::getSamplerId)
 			.uniform1b(PER_FRAME, "hideGUI", () -> client.options.hudHidden)
 			.uniform1i(ONCE, "noisetex", () -> 15)
+			.uniform1i(ONCE, "normals", () -> 2)
+			.uniform1i(ONCE, "specular", () -> 3)
 			.uniform1i(ONCE, "shadowtex0", () -> 4)
 			.uniform1i(ONCE, "shadowtex1", () -> 5)
 			.uniform1f(PER_FRAME, "eyeAltitude", () -> Objects.requireNonNull(client.getCameraEntity()).getEyeY())