feat: Implement BillboardToWorldZ emitters

src/render/shaders.cpp

@@ -76,6 +76,7 @@ layout(std140) uniform General {
     uniform vec2 uBillboardSize;
     uniform vec4 uParticleCenter;
     uniform int uBillboardFrame;
+    uniform bool uBillboardToWorldZ;
 };
 
 layout(std140) uniform Lighting {
@@ -165,6 +166,9 @@ void main() {
 )END";
 
 static const GLchar kSourceVertexBillboard[] = R"END(
+const vec3 RIGHT = vec3(1.0, 0.0, 0.0);
+const vec3 FORWARD = vec3(0.0, 1.0, 0.0);
+
 uniform mat4 uProjection;
 uniform mat4 uView;
 
@@ -174,13 +178,23 @@ layout(location = 2) in vec2 aTexCoords;
 out vec2 fragTexCoords;
 
 void main() {
-    vec3 cameraRight = vec3(uView[0][0], uView[1][0], uView[2][0]);
-    vec3 cameraUp = vec3(uView[0][1], uView[1][1], uView[2][1]);
+    vec3 position;
 
-    vec3 position =
-        uParticleCenter.xyz +
-        cameraRight * aPosition.x * uBillboardSize.x +
-        cameraUp * aPosition.y * uBillboardSize.y;
+    if (uBillboardToWorldZ) {
+        position = 
+            uParticleCenter.xyz +
+            RIGHT * aPosition.x * uBillboardSize.x +
+            FORWARD * aPosition.y * uBillboardSize.y;
+
+    } else {
+        vec3 cameraRight = vec3(uView[0][0], uView[1][0], uView[2][0]);
+        vec3 cameraUp = vec3(uView[0][1], uView[1][1], uView[2][1]);
+
+        position =
+            uParticleCenter.xyz +
+            cameraRight * aPosition.x * uBillboardSize.x +
+            cameraUp * aPosition.y * uBillboardSize.y;
+    }
 
     gl_Position = uProjection * uView * vec4(position, 1.0);
     fragTexCoords = aTexCoords;

src/render/shaders.h

@@ -93,7 +93,8 @@ struct GeneralUniforms {
     glm::vec2 billboardSize { 0.0f };
     glm::vec4 particleCenter { 0.0f };
     int billboardFrame { 0 };
-    char padding3[12];
+    int billboardToWorldZ { 0 };
+    char padding3[8];
 };
 
 struct SkeletalUniforms {

src/scene/node/modelscenenode.cpp

@@ -59,6 +59,7 @@ static bool validateEmitter(const Emitter &emitter) {
 
     switch (emitter.renderType()) {
         case Emitter::RenderType::Normal:
+        case Emitter::RenderType::BillboardToWorldZ:
             break;
         default:
             warn("validateEmitter: unsupported render type: " + to_string(static_cast<int>(emitter.renderType())));

src/scene/node/particlenode.cpp

@@ -103,6 +103,7 @@ void ParticleSceneNode::renderSingle(bool shadowPass) const {
     locals.general.billboardSize = glm::vec2(_size);
     locals.general.particleCenter = _absoluteTransform[3];
     locals.general.billboardFrame = _frame;
+    locals.general.billboardToWorldZ = _emitter->renderType() == Emitter::RenderType::BillboardToWorldZ;
 
     Shaders::instance().activate(ShaderProgram::BillboardBillboard, locals);