From 4fc3689dcc93863bcdec06a64ec8e240b50c6f2f Mon Sep 17 00:00:00 2001
From: Kelsi <kelsihates2fa@gmail.com>
Date: Sat, 21 Feb 2026 21:57:16 -0800
Subject: [PATCH] Fix sky and clouds orientation for Z-up world coordinates

Skybox: replace sphere-mesh approach with a fullscreen triangle that
reconstructs the world-space ray direction analytically via inverse
projection/view matrices. Eliminates clip.w=0 degeneracy at the horizon
and correctly maps altitude to dir.z in the Z-up coordinate system.

Clouds: hemisphere mesh was storing altitude in aPos.y (Y-up convention);
the Z-up view matrix projected this sideways, making clouds appear
vertical. Store altitude in aPos.z and update the fragment shader to
read dir.z as altitude and dir.xy as the horizontal UV plane.
---
 assets/shaders/clouds.frag.glsl |   4 +-
 assets/shaders/clouds.frag.spv  | Bin 5356 -> 5372 bytes
 assets/shaders/skybox.frag.glsl |  23 ++++++-
 assets/shaders/skybox.frag.spv  | Bin 2532 -> 3568 bytes
 assets/shaders/skybox.vert.glsl |  27 ++------
 assets/shaders/skybox.vert.spv  | Bin 2756 -> 1220 bytes
 include/rendering/skybox.hpp    |  15 +---
 src/rendering/clouds.cpp        |   8 +--
 src/rendering/skybox.cpp        | 117 ++------------------------------
 9 files changed, 39 insertions(+), 155 deletions(-)

diff --git a/assets/shaders/clouds.frag.glsl b/assets/shaders/clouds.frag.glsl
index 419e0b7b..fec28507 100644
--- a/assets/shaders/clouds.frag.glsl
+++ b/assets/shaders/clouds.frag.glsl
@@ -38,10 +38,10 @@ float fbm(vec2 p) {
 
 void main() {
     vec3 dir = normalize(vWorldDir);
-    float altitude = dir.y;
+    float altitude = dir.z;   // Z is up in the Z-up world coordinate system
     if (altitude < 0.0) discard;
 
-    vec2 uv = dir.xz / (altitude + 0.001);
+    vec2 uv = dir.xy / (altitude + 0.001);  // XY is the horizontal plane
     uv += push.windOffset;
 
     float cloud1 = fbm(uv * 0.8);
diff --git a/assets/shaders/clouds.frag.spv b/assets/shaders/clouds.frag.spv
index b1118d83e373e82aec13dfc6476ea52aee338654..7d09eb467a3823429dcd040c36878a0ecf280f69 100644
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diff --git a/assets/shaders/skybox.frag.glsl b/assets/shaders/skybox.frag.glsl
index 179dd9c3..b2054e15 100644
--- a/assets/shaders/skybox.frag.glsl
+++ b/assets/shaders/skybox.frag.glsl
@@ -19,13 +19,30 @@ layout(push_constant) uniform Push {
     float timeOfDay;
 } push;
 
-layout(location = 0) in vec3 WorldPos;
-layout(location = 1) in float Altitude;
+layout(location = 0) in vec2 TexCoord;
 
 layout(location = 0) out vec4 outColor;
 
 void main() {
-    float t = clamp(Altitude, 0.0, 1.0);
+    // Reconstruct world-space ray direction from screen position.
+    // TexCoord is [0,1]^2; convert to NDC [-1,1]^2.
+    float ndcX =  TexCoord.x * 2.0 - 1.0;
+    float ndcY = -(TexCoord.y * 2.0 - 1.0);  // flip Y: Vulkan NDC Y-down, but projection already flipped
+
+    // Unproject to view space using focal lengths from projection matrix.
+    // projection[0][0] = 2*near/(right-left) = 1/tan(fovX/2)
+    // projection[1][1] = 2*near/(top-bottom)  (already negated for Vulkan Y-flip)
+    // We want the original magnitude, so take abs to get the focal length.
+    vec3 viewDir = vec3(ndcX / projection[0][0],
+                        ndcY / abs(projection[1][1]),
+                        -1.0);
+
+    // Rotate to world space: view = R*T, so R^-1 = R^T = transpose(mat3(view))
+    mat3 invViewRot = transpose(mat3(view));
+    vec3 worldDir = normalize(invViewRot * viewDir);
+
+    // worldDir.z = sin(elevation); +1 = zenith, 0 = horizon, -1 = nadir
+    float t = clamp(worldDir.z, 0.0, 1.0);
     t = pow(t, 1.5);
     vec3 sky = mix(push.horizonColor.rgb, push.zenithColor.rgb, t);
     float scatter = max(0.0, 1.0 - t * 2.0) * 0.15;
diff --git a/assets/shaders/skybox.frag.spv b/assets/shaders/skybox.frag.spv
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diff --git a/assets/shaders/skybox.vert.glsl b/assets/shaders/skybox.vert.glsl
index 95462764..d1df7d5a 100644
--- a/assets/shaders/skybox.vert.glsl
+++ b/assets/shaders/skybox.vert.glsl
@@ -1,27 +1,12 @@
 #version 450
 
-layout(set = 0, binding = 0) uniform PerFrame {
-    mat4 view;
-    mat4 projection;
-    mat4 lightSpaceMatrix;
-    vec4 lightDir;
-    vec4 lightColor;
-    vec4 ambientColor;
-    vec4 viewPos;
-    vec4 fogColor;
-    vec4 fogParams; // x=fogStart, y=fogEnd, z=time
-    vec4 shadowParams; // x=enabled, y=strength
-};
+// Fullscreen triangle sky — no vertex buffer, no mesh.
+// Draws 3 vertices covering the entire screen, depth forced to 1.0 (far plane).
 
-layout(location = 0) in vec3 aPos;
-
-layout(location = 0) out vec3 WorldPos;
-layout(location = 1) out float Altitude;
+layout(location = 0) out vec2 TexCoord;
 
 void main() {
-    WorldPos = aPos;
-    Altitude = aPos.y;
-    mat4 rotView = mat4(mat3(view)); // strip translation
-    vec4 pos = projection * rotView * vec4(aPos, 1.0);
-    gl_Position = pos.xyww; // force far plane
+    // Produces triangle covering NDC [-1,1]² with depth = 1.0 (far)
+    TexCoord = vec2((gl_VertexIndex << 1) & 2, gl_VertexIndex & 2);
+    gl_Position = vec4(TexCoord * 2.0 - 1.0, 1.0, 1.0);
 }
diff --git a/assets/shaders/skybox.vert.spv b/assets/shaders/skybox.vert.spv
index 8203b21fe00aa526cb6e293d6cfeb1d5c3eb1e69..bc7f0006e5a3ae70599ae49b5b2e1f737d3768e4 100644
GIT binary patch
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diff --git a/include/rendering/skybox.hpp b/include/rendering/skybox.hpp
index 42ed67db..23a79db9 100644
--- a/include/rendering/skybox.hpp
+++ b/include/rendering/skybox.hpp
@@ -13,8 +13,9 @@ class VkContext;
 /**
  * Skybox renderer
  *
- * Renders an atmospheric sky dome with gradient colors.
- * The sky uses a dome/sphere approach for realistic appearance.
+ * Renders an atmospheric sky gradient using a fullscreen triangle.
+ * No vertex buffer: 3 vertices cover the entire screen via gl_VertexIndex.
+ * World-space ray direction is reconstructed from the inverse view+projection.
  */
 class Skybox {
 public:
@@ -62,9 +63,6 @@ public:
     glm::vec3 getHorizonColor(float time) const;
 
 private:
-    void createSkyDome();
-    void destroySkyDome();
-
     glm::vec3 getSkyColor(float altitude, float time) const;
     glm::vec3 getZenithColor(float time) const;
 
@@ -73,13 +71,6 @@ private:
     VkPipeline pipeline = VK_NULL_HANDLE;
     VkPipelineLayout pipelineLayout = VK_NULL_HANDLE;
 
-    VkBuffer vertexBuffer = VK_NULL_HANDLE;
-    VmaAllocation vertexAlloc = VK_NULL_HANDLE;
-    VkBuffer indexBuffer = VK_NULL_HANDLE;
-    VmaAllocation indexAlloc = VK_NULL_HANDLE;
-
-    int indexCount = 0;
-
     float timeOfDay = 12.0f;  // Default: noon
     float timeSpeed = 1.0f;   // 1.0 = 1 hour per real second
     bool timeProgressionEnabled = false;
diff --git a/src/rendering/clouds.cpp b/src/rendering/clouds.cpp
index 11193217..9b90d4a0 100644
--- a/src/rendering/clouds.cpp
+++ b/src/rendering/clouds.cpp
@@ -202,17 +202,17 @@ void Clouds::generateMesh() {
     vertices_.clear();
     indices_.clear();
 
-    // Upper hemisphere
+    // Upper hemisphere — Z-up world: altitude goes into Z, horizontal spread in X/Y
     for (int ring = 0; ring <= RINGS; ++ring) {
         float phi        = (ring / static_cast<float>(RINGS)) * (static_cast<float>(M_PI) * 0.5f);
-        float y          = RADIUS * std::cos(phi);
+        float altZ       = RADIUS * std::cos(phi);   // altitude → world Z (up)
         float ringRadius = RADIUS * std::sin(phi);
 
         for (int seg = 0; seg <= SEGMENTS; ++seg) {
             float theta = (seg / static_cast<float>(SEGMENTS)) * (2.0f * static_cast<float>(M_PI));
             float x = ringRadius * std::cos(theta);
-            float z = ringRadius * std::sin(theta);
-            vertices_.push_back(glm::vec3(x, y, z));
+            float y = ringRadius * std::sin(theta);
+            vertices_.push_back(glm::vec3(x, y, altZ));
         }
     }
 
diff --git a/src/rendering/skybox.cpp b/src/rendering/skybox.cpp
index 368c7cbe..a51e2706 100644
--- a/src/rendering/skybox.cpp
+++ b/src/rendering/skybox.cpp
@@ -3,11 +3,9 @@
 #include "rendering/vk_shader.hpp"
 #include "rendering/vk_pipeline.hpp"
 #include "rendering/vk_frame_data.hpp"
-#include "rendering/vk_utils.hpp"
 #include "core/logger.hpp"
 #include <glm/gtc/matrix_transform.hpp>
 #include <cmath>
-#include <vector>
 
 namespace wowee {
 namespace rendering {
@@ -54,18 +52,7 @@ bool Skybox::initialize(VkContext* ctx, VkDescriptorSetLayout perFrameLayout) {
         return false;
     }
 
-    // Vertex input: position only (vec3), stride = 3 * sizeof(float)
-    VkVertexInputBindingDescription binding{};
-    binding.binding = 0;
-    binding.stride = 3 * sizeof(float);
-    binding.inputRate = VK_VERTEX_INPUT_RATE_VERTEX;
-
-    VkVertexInputAttributeDescription posAttr{};
-    posAttr.location = 0;
-    posAttr.binding = 0;
-    posAttr.format = VK_FORMAT_R32G32B32_SFLOAT;
-    posAttr.offset = 0;
-
+    // Fullscreen triangle — no vertex buffer, no vertex input.
     // Dynamic viewport and scissor
     std::vector<VkDynamicState> dynamicStates = {
         VK_DYNAMIC_STATE_VIEWPORT,
@@ -74,7 +61,7 @@ bool Skybox::initialize(VkContext* ctx, VkDescriptorSetLayout perFrameLayout) {
 
     pipeline = PipelineBuilder()
         .setShaders(vertStage, fragStage)
-        .setVertexInput({binding}, {posAttr})
+        .setVertexInput({}, {})
         .setTopology(VK_PRIMITIVE_TOPOLOGY_TRIANGLE_LIST)
         .setRasterization(VK_POLYGON_MODE_FILL, VK_CULL_MODE_NONE)
         .setDepthTest(true, false, VK_COMPARE_OP_LESS_OR_EQUAL)  // depth test on, write off, LEQUAL for far plane
@@ -93,16 +80,11 @@ bool Skybox::initialize(VkContext* ctx, VkDescriptorSetLayout perFrameLayout) {
         return false;
     }
 
-    // Create sky dome mesh and upload to GPU
-    createSkyDome();
-
     LOG_INFO("Skybox initialized");
     return true;
 }
 
 void Skybox::shutdown() {
-    destroySkyDome();
-
     if (vkCtx) {
         VkDevice device = vkCtx->getDevice();
         if (pipeline != VK_NULL_HANDLE) {
@@ -149,15 +131,8 @@ void Skybox::render(VkCommandBuffer cmd, VkDescriptorSet perFrameSet, float time
         VK_SHADER_STAGE_VERTEX_BIT | VK_SHADER_STAGE_FRAGMENT_BIT,
         0, sizeof(push), &push);
 
-    // Bind vertex buffer
-    VkDeviceSize offset = 0;
-    vkCmdBindVertexBuffers(cmd, 0, 1, &vertexBuffer, &offset);
-
-    // Bind index buffer
-    vkCmdBindIndexBuffer(cmd, indexBuffer, 0, VK_INDEX_TYPE_UINT32);
-
-    // Draw
-    vkCmdDrawIndexed(cmd, static_cast<uint32_t>(indexCount), 1, 0, 0, 0);
+    // Draw fullscreen triangle — no vertex buffer needed
+    vkCmdDraw(cmd, 3, 1, 0, 0);
 }
 
 void Skybox::update(float deltaTime) {
@@ -179,90 +154,6 @@ void Skybox::setTimeOfDay(float time) {
     timeOfDay = time;
 }
 
-void Skybox::createSkyDome() {
-    // Create an extended dome that goes below horizon for better coverage
-    const int rings = 16;      // Vertical resolution
-    const int sectors = 32;    // Horizontal resolution
-    const float radius = 2000.0f;  // Large enough to cover view without looking curved
-
-    std::vector<float> vertices;
-    std::vector<uint32_t> indices;
-
-    // Generate vertices - extend slightly below horizon
-    const float minPhi = -M_PI / 12.0f;  // Start 15° below horizon
-    const float maxPhi = M_PI / 2.0f;     // End at zenith
-    for (int ring = 0; ring <= rings; ring++) {
-        float phi = minPhi + (maxPhi - minPhi) * (static_cast<float>(ring) / rings);
-        float y = radius * std::sin(phi);
-        float ringRadius = radius * std::cos(phi);
-
-        for (int sector = 0; sector <= sectors; sector++) {
-            float theta = (2.0f * M_PI) * (static_cast<float>(sector) / sectors);
-            float x = ringRadius * std::cos(theta);
-            float z = ringRadius * std::sin(theta);
-
-            // Position
-            vertices.push_back(x);
-            vertices.push_back(z);  // Z up in WoW coordinates
-            vertices.push_back(y);
-        }
-    }
-
-    // Generate indices
-    for (int ring = 0; ring < rings; ring++) {
-        for (int sector = 0; sector < sectors; sector++) {
-            int current = ring * (sectors + 1) + sector;
-            int next = current + sectors + 1;
-
-            // Two triangles per quad
-            indices.push_back(current);
-            indices.push_back(next);
-            indices.push_back(current + 1);
-
-            indices.push_back(current + 1);
-            indices.push_back(next);
-            indices.push_back(next + 1);
-        }
-    }
-
-    indexCount = static_cast<int>(indices.size());
-
-    // Upload vertex buffer to GPU via staging
-    AllocatedBuffer vbuf = uploadBuffer(*vkCtx,
-        vertices.data(),
-        vertices.size() * sizeof(float),
-        VK_BUFFER_USAGE_VERTEX_BUFFER_BIT);
-    vertexBuffer = vbuf.buffer;
-    vertexAlloc  = vbuf.allocation;
-
-    // Upload index buffer to GPU via staging
-    AllocatedBuffer ibuf = uploadBuffer(*vkCtx,
-        indices.data(),
-        indices.size() * sizeof(uint32_t),
-        VK_BUFFER_USAGE_INDEX_BUFFER_BIT);
-    indexBuffer = ibuf.buffer;
-    indexAlloc  = ibuf.allocation;
-
-    LOG_DEBUG("Sky dome created: ", (rings + 1) * (sectors + 1), " vertices, ", indexCount / 3, " triangles");
-}
-
-void Skybox::destroySkyDome() {
-    if (!vkCtx) return;
-
-    VmaAllocator allocator = vkCtx->getAllocator();
-
-    if (vertexBuffer != VK_NULL_HANDLE) {
-        vmaDestroyBuffer(allocator, vertexBuffer, vertexAlloc);
-        vertexBuffer = VK_NULL_HANDLE;
-        vertexAlloc  = VK_NULL_HANDLE;
-    }
-    if (indexBuffer != VK_NULL_HANDLE) {
-        vmaDestroyBuffer(allocator, indexBuffer, indexAlloc);
-        indexBuffer = VK_NULL_HANDLE;
-        indexAlloc  = VK_NULL_HANDLE;
-    }
-}
-
 glm::vec3 Skybox::getHorizonColor(float time) const {
     // Time-based horizon colors
     // 0-6: Night (dark blue)