Vertex and attribute compression to reduce the size of the vertex format.

This allows Godot to automatically compress meshes to save a lot of bandwidth.

In general, this requires no interaction from the user and should result in
no noticable quality loss.

This scheme is not backwards compatible, so we have provided an upgrade
mechanism, and a mesh versioning mechanism.

Existing meshes can still be used as a result, but users can get a
performance boost by reimporting assets.

1 files changed, 52 insertions, 27 deletions

diff --git a/drivers/gles3/shaders/scene.glsl b/drivers/gles3/shaders/scene.glsl
index 0c1a20caed..c98b5f3ed7 100644
--- a/drivers/gles3/shaders/scene.glsl
+++ b/drivers/gles3/shaders/scene.glsl
@@ -52,8 +52,8 @@ ADDITIVE_SPOT = false
 
 /*
 from RenderingServer:
-ARRAY_VERTEX = 0, // RG32F or RGB32F (depending on 2D bit)
-ARRAY_NORMAL = 1, // RG16 octahedral compression
+ARRAY_VERTEX = 0, // RGB32F or RGBA16
+ARRAY_NORMAL = 1, // RG16 octahedral compression or RGBA16 normal + angle
 ARRAY_TANGENT = 2, // RG16 octahedral compression, sign stored in sign of G
 ARRAY_COLOR = 3, // RGBA8
 ARRAY_TEX_UV = 4, // RG32F
@@ -68,16 +68,16 @@ ARRAY_WEIGHTS = 11, // RGBA16UNORM (x2 if 8 weights)
 
 /* INPUT ATTRIBS */
 
-layout(location = 0) in highp vec3 vertex_attrib;
+// Always contains vertex position in XYZ, can contain tangent angle in W.
+layout(location = 0) in highp vec4 vertex_angle_attrib;
 /* clang-format on */
 
 #ifdef NORMAL_USED
-layout(location = 1) in vec2 normal_attrib;
+// Contains Normal/Axis in RG, can contain tangent in BA.
+layout(location = 1) in vec4 axis_tangent_attrib;
 #endif
 
-#if defined(TANGENT_USED) || defined(NORMAL_MAP_USED) || defined(LIGHT_ANISOTROPY_USED)
-layout(location = 2) in vec2 tangent_attrib;
-#endif
+// location 2 is unused.
 
 #if defined(COLOR_USED)
 layout(location = 3) in vec4 color_attrib;
@@ -122,6 +122,16 @@ vec3 oct_to_vec3(vec2 e) {
 	return normalize(v);
 }
 
+void axis_angle_to_tbn(vec3 axis, float angle, out vec3 tangent, out vec3 binormal, out vec3 normal) {
+	float c = cos(angle);
+	float s = sin(angle);
+	vec3 omc_axis = (1.0 - c) * axis;
+	vec3 s_axis = s * axis;
+	tangent = omc_axis.xxx * axis + vec3(c, -s_axis.z, s_axis.y);
+	binormal = omc_axis.yyy * axis + vec3(s_axis.z, c, -s_axis.x);
+	normal = omc_axis.zzz * axis + vec3(-s_axis.y, s_axis.x, c);
+}
+
 #ifdef USE_INSTANCING
 layout(location = 12) in highp vec4 instance_xform0;
 layout(location = 13) in highp vec4 instance_xform1;
@@ -228,10 +238,9 @@ multiview_data;
 #endif
 
 uniform highp mat4 world_transform;
-
-#ifdef USE_LIGHTMAP
-uniform highp vec4 lightmap_uv_rect;
-#endif
+uniform highp vec3 compressed_aabb_position;
+uniform highp vec3 compressed_aabb_size;
+uniform highp vec4 uv_scale;
 
 /* Varyings */
 
@@ -248,13 +257,9 @@ out vec4 color_interp;
 out vec2 uv_interp;
 #endif
 
-#if defined(UV2_USED)
-out vec2 uv2_interp;
-#else
-#ifdef USE_LIGHTMAP
+#if defined(UV2_USED) || defined(USE_LIGHTMAP)
 out vec2 uv2_interp;
 #endif
-#endif
 
 #if defined(TANGENT_USED) || defined(NORMAL_MAP_USED) || defined(LIGHT_ANISOTROPY_USED)
 out vec3 tangent_interp;
@@ -294,7 +299,7 @@ layout(std140) uniform MaterialUniforms { // ubo:3
 invariant gl_Position;
 
 void main() {
-	highp vec3 vertex = vertex_attrib;
+	highp vec3 vertex = vertex_angle_attrib.xyz * compressed_aabb_size + compressed_aabb_position;
 
 	highp mat4 model_matrix = world_transform;
 #ifdef USE_INSTANCING
@@ -303,15 +308,30 @@ void main() {
 #endif
 
 #ifdef NORMAL_USED
-	vec3 normal = oct_to_vec3(normal_attrib * 2.0 - 1.0);
+	vec3 normal = oct_to_vec3(axis_tangent_attrib.xy * 2.0 - 1.0);
 #endif
 	highp mat3 model_normal_matrix = mat3(model_matrix);
 
-#if defined(TANGENT_USED) || defined(NORMAL_MAP_USED) || defined(LIGHT_ANISOTROPY_USED)
-	vec2 signed_tangent_attrib = tangent_attrib * 2.0 - 1.0;
-	vec3 tangent = oct_to_vec3(vec2(signed_tangent_attrib.x, abs(signed_tangent_attrib.y) * 2.0 - 1.0));
-	float binormalf = sign(signed_tangent_attrib.y);
-	vec3 binormal = normalize(cross(normal, tangent) * binormalf);
+#if defined(NORMAL_USED) || defined(TANGENT_USED) || defined(NORMAL_MAP_USED) || defined(LIGHT_ANISOTROPY_USED)
+
+	vec3 binormal;
+	float binormal_sign;
+	vec3 tangent;
+	if (axis_tangent_attrib.z > 0.0 || axis_tangent_attrib.w < 1.0) {
+		// Uncompressed format.
+		vec2 signed_tangent_attrib = axis_tangent_attrib.zw * 2.0 - 1.0;
+		tangent = oct_to_vec3(vec2(signed_tangent_attrib.x, abs(signed_tangent_attrib.y) * 2.0 - 1.0));
+		binormal_sign = sign(signed_tangent_attrib.y);
+		binormal = normalize(cross(normal, tangent) * binormal_sign);
+	} else {
+		// Compressed format.
+		float angle = vertex_angle_attrib.w;
+		binormal_sign = angle > 0.5 ? 1.0 : -1.0; // 0.5 does not exist in UNORM16, so values are either greater or smaller.
+		angle = abs(angle * 2.0 - 1.0) * M_PI; // 0.5 is basically zero, allowing to encode both signs reliably.
+		vec3 axis = normal;
+		axis_angle_to_tbn(axis, angle, tangent, binormal, normal);
+		binormal *= binormal_sign;
+	}
 #endif
 
 #if defined(COLOR_USED)
@@ -326,13 +346,18 @@ void main() {
 	uv_interp = uv_attrib;
 #endif
 
-#ifdef USE_LIGHTMAP
-	uv2_interp = lightmap_uv_rect.zw * uv2_attrib + lightmap_uv_rect.xy;
-#else
-#if defined(UV2_USED)
+#if defined(UV2_USED) || defined(USE_LIGHTMAP)
 	uv2_interp = uv2_attrib;
 #endif
+
+	if (uv_scale != vec4(0.0)) { // Compression enabled
+#ifdef UV_USED
+		uv_interp = (uv_interp - 0.5) * uv_scale.xy;
+#endif
+#if defined(UV2_USED) || defined(USE_LIGHTMAP)
+		uv2_interp = (uv2_interp - 0.5) * uv_scale.zw;
 #endif
+	}
 
 #if defined(OVERRIDE_POSITION)
 	highp vec4 position;