Fix issues when rendering panoramic sky in stereoscopic

drivers/gles3/rasterizer_scene_gles3.cpp

@@ -2349,22 +2349,7 @@ void RasterizerSceneGLES3::_draw_sky(RasterizerStorageGLES3::Sky *p_sky, const C
 	glDepthFunc(GL_LEQUAL);
 	glColorMask(1, 1, 1, 1);
 
-	float flip_sign = p_vflip ? -1 : 1;
-
-	Vector3 vertices[8] = {
-		Vector3(-1, -1 * flip_sign, 1),
-		Vector3(0, 1, 0),
-		Vector3(1, -1 * flip_sign, 1),
-		Vector3(1, 1, 0),
-		Vector3(1, 1 * flip_sign, 1),
-		Vector3(1, 0, 0),
-		Vector3(-1, 1 * flip_sign, 1),
-		Vector3(0, 0, 0)
-
-	};
-
-	//sky uv vectors
-	float vw, vh, zn;
+	// Camera
 	CameraMatrix camera;
 
 	if (p_custom_fov) {
@@ -2379,17 +2364,39 @@ void RasterizerSceneGLES3::_draw_sky(RasterizerStorageGLES3::Sky *p_sky, const C
 		camera = p_projection;
 	}
 
-	camera.get_viewport_size(vw, vh);
-	zn = p_projection.get_z_near();
+	float flip_sign = p_vflip ? -1 : 1;
 
-	for (int i = 0; i < 4; i++) {
+	/*
+		If matrix[2][0] or matrix[2][1] we're dealing with an asymmetrical projection matrix. This is the case for stereoscopic rendering (i.e. VR).
+		To ensure the image rendered is perspective correct we need to move some logic into the shader. For this the USE_ASYM_PANO option is introduced.
+		It also means the uv coordinates are ignored in this mode and we don't need our loop.
+	*/
+	bool asymmetrical = ((camera.matrix[2][0] != 0.0) || (camera.matrix[2][1] != 0.0));
 
-		Vector3 uv = vertices[i * 2 + 1];
-		uv.x = (uv.x * 2.0 - 1.0) * vw;
-		uv.y = -(uv.y * 2.0 - 1.0) * vh;
-		uv.z = -zn;
-		vertices[i * 2 + 1] = p_transform.basis.xform(uv).normalized();
-		vertices[i * 2 + 1].z = -vertices[i * 2 + 1].z;
+	Vector3 vertices[8] = {
+		Vector3(-1, -1 * flip_sign, 1),
+		Vector3(0, 1, 0),
+		Vector3(1, -1 * flip_sign, 1),
+		Vector3(1, 1, 0),
+		Vector3(1, 1 * flip_sign, 1),
+		Vector3(1, 0, 0),
+		Vector3(-1, 1 * flip_sign, 1),
+		Vector3(0, 0, 0)
+	};
+
+	if (!asymmetrical) {
+		float vw, vh, zn;
+		camera.get_viewport_size(vw, vh);
+		zn = p_projection.get_z_near();
+
+		for (int i = 0; i < 4; i++) {
+			Vector3 uv = vertices[i * 2 + 1];
+			uv.x = (uv.x * 2.0 - 1.0) * vw;
+			uv.y = -(uv.y * 2.0 - 1.0) * vh;
+			uv.z = -zn;
+			vertices[i * 2 + 1] = p_transform.basis.xform(uv).normalized();
+			vertices[i * 2 + 1].z = -vertices[i * 2 + 1].z;
+		}
 	}
 
 	glBindBuffer(GL_ARRAY_BUFFER, state.sky_verts);
@@ -2398,16 +2405,24 @@ void RasterizerSceneGLES3::_draw_sky(RasterizerStorageGLES3::Sky *p_sky, const C
 
 	glBindVertexArray(state.sky_array);
 
-	storage->shaders.copy.set_conditional(CopyShaderGLES3::USE_PANORAMA, true);
+	storage->shaders.copy.set_conditional(CopyShaderGLES3::USE_ASYM_PANO, asymmetrical);
+	storage->shaders.copy.set_conditional(CopyShaderGLES3::USE_PANORAMA, !asymmetrical);
 	storage->shaders.copy.set_conditional(CopyShaderGLES3::USE_MULTIPLIER, true);
 	storage->shaders.copy.bind();
 	storage->shaders.copy.set_uniform(CopyShaderGLES3::MULTIPLIER, p_energy);
+	if (asymmetrical) {
+		// pack the bits we need from our projection matrix
+		storage->shaders.copy.set_uniform(CopyShaderGLES3::ASYM_PROJ, camera.matrix[2][0], camera.matrix[0][0], camera.matrix[2][1], camera.matrix[1][1]);
+		///@TODO I couldn't get mat3 + p_transform.basis to work, that would be better here.
+		storage->shaders.copy.set_uniform(CopyShaderGLES3::PANO_TRANSFORM, p_transform);
+	}
 
 	glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
 
 	glBindVertexArray(0);
 	glColorMask(1, 1, 1, 1);
 
+	storage->shaders.copy.set_conditional(CopyShaderGLES3::USE_ASYM_PANO, false);
 	storage->shaders.copy.set_conditional(CopyShaderGLES3::USE_MULTIPLIER, false);
 	storage->shaders.copy.set_conditional(CopyShaderGLES3::USE_PANORAMA, false);
 }

drivers/gles3/shaders/copy.glsl

@@ -27,6 +27,8 @@ void main() {
 
 #if defined(USE_CUBEMAP) || defined(USE_PANORAMA)
 	cube_interp = cube_in;
+#elif defined(USE_ASYM_PANO)
+	uv_interp = vertex_attrib.xy;
 #else
 	uv_interp = uv_in;
 #ifdef V_FLIP
@@ -59,6 +61,11 @@ in vec3 cube_interp;
 in vec2 uv_interp;
 #endif
 
+#ifdef USE_ASYM_PANO
+uniform highp mat4 pano_transform;
+uniform highp vec4 asym_proj;
+#endif
+
 #ifdef USE_CUBEMAP
 uniform samplerCube source_cube; //texunit:0
 #else
@@ -70,7 +77,7 @@ uniform sampler2D source; //texunit:0
 uniform float multiplier;
 #endif
 
-#ifdef USE_PANORAMA
+#if defined(USE_PANORAMA) || defined(USE_ASYM_PANO)
 
 vec4 texturePanorama(vec3 normal,sampler2D pano ) {
 
@@ -122,6 +129,21 @@ void main() {
 
 	vec4 color = texturePanorama(  normalize(cube_interp), source );
 
+#elif defined(USE_ASYM_PANO)
+
+	// When an assymetrical projection matrix is used (applicable for stereoscopic rendering i.e. VR) we need to do this calculation per fragment to get a perspective correct result. 
+	// Note that we're ignoring the x-offset for IPD, with Z sufficiently in the distance it becomes neglectible, as a result we could probably just set cube_normal.z to -1.
+	// The Matrix[2][0] (= asym_proj.x) and Matrix[2][1] (= asym_proj.z) values are what provide the right shift in the image.
+
+	vec3 cube_normal;
+	cube_normal.z = -1000000.0;
+	cube_normal.x = (cube_normal.z * (-uv_interp.x - asym_proj.x)) / asym_proj.y;
+	cube_normal.y = (cube_normal.z * (-uv_interp.y - asym_proj.z)) / asym_proj.a;
+	cube_normal = mat3(pano_transform) * cube_normal;
+	cube_normal.z = -cube_normal.z;
+
+	vec4 color = texturePanorama(  normalize(cube_normal.xyz), source );
+
 #elif defined(USE_CUBEMAP)
 	vec4 color = texture( source_cube,  normalize(cube_interp) );