feat: add enemy health bar system

config/app.jsonc

@@ -180,6 +180,18 @@
             }
         },
         "game": {
+            "enemyHealthBars": {
+                "enabled": true,
+                "maxDistance": 22.0,
+                "colors": {
+                    "low": [0.84, 0.18, 0.24, 0.96],
+                    "mid": [0.96, 0.76, 0.25, 0.96],
+                    "high": [0.28, 0.84, 0.45, 0.96],
+                    "border": [0.02, 0.03, 0.05, 0.92],
+                    "background": [0.12, 0.14, 0.18, 0.88],
+                    "highlight": [1.0, 1.0, 1.0, 0.12]
+                }
+            },
             "enemySpawner": {
                 "spawnPoints": [
                     [30.0, 0.0, 30.0],

src/common/systems/ui-renderer.hpp

@@ -0,0 +1,107 @@
+#pragma once
+
+#include <glad/gl.h>
+
+#include <components/camera.hpp>
+#include <ecs/world.hpp>
+#include <glm/gtc/matrix_transform.hpp>
+#include <glm/vec2.hpp>
+#include <glm/vec4.hpp>
+#include <vector>
+
+#include "../asset-loader.hpp"
+#include "../material/material.hpp"
+#include "../mesh/mesh.hpp"
+#include "../mesh/vertex.hpp"
+#include "../shader/shader.hpp"
+
+namespace our {
+
+    struct ScreenPoint {
+        glm::vec2 position;
+        float depth;
+        bool visible;
+    };
+
+    class UIRenderer {
+        Mesh* quad = nullptr;
+        TintedMaterial* material = nullptr;
+
+        static Vertex makeVertex(const glm::vec3& position, const glm::vec2& texCoord) {
+            Vertex vertex{};
+            vertex.position = position;
+            vertex.color = {255, 255, 255, 255};
+            vertex.tex_coord = texCoord;
+            vertex.normal = {0.0f, 0.0f, 1.0f};
+            return vertex;
+        }
+
+    public:
+        void initialize() {
+            material = new TintedMaterial();
+            material->shader = AssetLoader<ShaderProgram>::get("tinted");
+            material->pipelineState.blending.enabled = true;
+            material->pipelineState.blending.sourceFactor = GL_SRC_ALPHA;
+            material->pipelineState.blending.destinationFactor = GL_ONE_MINUS_SRC_ALPHA;
+            material->pipelineState.depthTesting.enabled = false;
+            material->pipelineState.faceCulling.enabled = false;
+            material->pipelineState.depthMask = false;
+
+            std::vector<Vertex> vertices = {
+                makeVertex({0.0f, 0.0f, 0.0f}, {0.0f, 1.0f}),
+                makeVertex({1.0f, 0.0f, 0.0f}, {1.0f, 1.0f}),
+                makeVertex({1.0f, 1.0f, 0.0f}, {1.0f, 0.0f}),
+                makeVertex({0.0f, 1.0f, 0.0f}, {0.0f, 0.0f}),
+            };
+            std::vector<unsigned int> elements = {0, 1, 2, 2, 3, 0};
+            quad = new Mesh(vertices, elements);
+        }
+
+        void destroy() {
+            delete quad;
+            delete material;
+            quad = nullptr;
+            material = nullptr;
+        }
+
+        glm::mat4 overlayProjection(glm::ivec2 framebufferSize) const {
+            return glm::ortho(0.0f, static_cast<float>(framebufferSize.x), static_cast<float>(framebufferSize.y), 0.0f,
+                              1.0f, -1.0f);
+        }
+
+        void drawRect(const glm::mat4& projection, const glm::vec2& position, const glm::vec2& size,
+                      const glm::vec4& color) const {
+            if (!(quad && material && material->shader)) return;
+            if (size.x <= 0.0f || size.y <= 0.0f || color.a <= 0.0f) return;
+
+            material->tint = color;
+            material->setup();
+            material->shader->set("transform", projection * glm::translate(glm::mat4(1.0f), glm::vec3(position, 0.0f)) *
+                                                   glm::scale(glm::mat4(1.0f), glm::vec3(size, 1.0f)));
+            quad->draw();
+        }
+
+        static ScreenPoint worldToScreen(const glm::vec3& worldPos, const glm::mat4& viewProj,
+                                         glm::ivec2 framebufferSize, float frustumMargin = 1.1f) {
+            ScreenPoint result{{0.0f, 0.0f}, 0.0f, false};
+
+            glm::vec4 clip = viewProj * glm::vec4(worldPos, 1.0f);
+            if (clip.w <= 0.0f) return result;  // behind camera
+
+            glm::vec3 ndc = glm::vec3(clip) / clip.w;
+            if (ndc.z < -1.0f || ndc.z > 1.0f) return result;
+            if (ndc.x < -frustumMargin || ndc.x > frustumMargin) return result;
+            if (ndc.y < -frustumMargin || ndc.y > frustumMargin) return result;
+
+            result.position = {
+                (ndc.x * 0.5f + 0.5f) * framebufferSize.x,
+                (1.0f - (ndc.y * 0.5f + 0.5f)) * framebufferSize.y,
+            };
+
+            result.depth = ndc.z;
+            result.visible = true;
+            return result;
+        }
+    };
+
+}  // namespace our

src/game/components/health.cpp

@@ -1,13 +1,21 @@
 #include "health.hpp"
 
+#include <algorithm>
+
 namespace gameplay {
 
     void HealthComponent::deserialize(const nlohmann::json& data) {
         if (!data.is_object()) return;
         maxHealth = data.value("maxHealth", maxHealth);
         currentHealth = data.contains("currentHealth") ? data["currentHealth"].get<float>() : maxHealth;
         invulnerabilityTimer = data.value("invulnerabilityTimer", invulnerabilityTimer);
+        damageRevealTimer = data.value("damageRevealTimer", damageRevealTimer);
         isDead = data.value("isDead", isDead);
     }
 
+    float HealthComponent::getHealthRatio() const {
+        if (maxHealth <= 0.0f) return 0.0f;
+        return std::clamp(currentHealth / maxHealth, 0.0f, 1.0f);
+    }
+
 }  // namespace gameplay

src/game/components/health.hpp

@@ -9,8 +9,11 @@ namespace gameplay {
         float maxHealth = 100.0f;
         float currentHealth = 100.0f;
         float invulnerabilityTimer = 0.0f;
+        float damageRevealTimer = 0.0f;
         bool isDead = false;
 
+        float getHealthRatio() const;
+
         static std::string getID() {
             return "Health";
         }

src/game/systems/enemy-health-bar.hpp

@@ -0,0 +1,154 @@
+#pragma once
+
+#include <algorithm>
+#include <application.hpp>
+#include <cmath>
+#include <deserialize-utils.hpp>
+#include <ecs/world.hpp>
+#include <glm/common.hpp>
+#include <glm/geometric.hpp>
+#include <glm/vec2.hpp>
+#include <glm/vec3.hpp>
+#include <glm/vec4.hpp>
+#include <json/json.hpp>
+#include <systems/ui-renderer.hpp>
+
+#include "../components/collider.hpp"
+#include "../components/enemy.hpp"
+#include "../components/health.hpp"
+
+namespace gameplay {
+
+    class EnemyHealthBarSystem {
+        struct Config {
+            bool enabled = true;
+            float maxDistance = 24.0f;
+            glm::vec4 lowColor = {0.84f, 0.18f, 0.24f, 0.96f};
+            glm::vec4 midColor = {0.96f, 0.76f, 0.25f, 0.96f};
+            glm::vec4 highColor = {0.28f, 0.84f, 0.45f, 0.96f};
+            glm::vec4 borderColor = {0.02f, 0.03f, 0.05f, 0.92f};
+            glm::vec4 backgroundColor = {0.12f, 0.14f, 0.18f, 0.88f};
+            glm::vec4 highlightColor = {1.0f, 1.0f, 1.0f, 0.12f};
+        } config;
+
+        static void deserializeColor(const nlohmann::json& colorConfig, const char* key, glm::vec4& color) {
+            if (!(colorConfig.contains(key) && colorConfig[key].is_array())) return;
+
+            const auto& value = colorConfig[key];
+            if (value.size() == 3) {
+                color = glm::vec4(value.get<glm::vec3>(), color.a);
+            } else if (value.size() == 4) {
+                color = value.get<glm::vec4>();
+            }
+        }
+
+        static float estimateBarHeight(const our::Entity* entity, const ColliderComponent* collider) {
+            float scaleHeight = std::max(std::abs(entity->localTransform.scale.y) * 1.2f, 1.0f);
+            if (!collider) return scaleHeight;
+
+            float colliderHeight = collider->radius * 2.0f;
+            if (collider->shape == ColliderShape::Capsule) colliderHeight = std::max(colliderHeight, collider->height);
+
+            return std::max(colliderHeight, scaleHeight);
+        }
+
+    public:
+        void deserialize(const nlohmann::json& sceneConfig) {
+            if (!(sceneConfig.contains("game") && sceneConfig["game"].contains("enemyHealthBars"))) return;
+
+            const auto& healthBarConfig = sceneConfig["game"]["enemyHealthBars"];
+            if (!healthBarConfig.is_object()) return;
+
+            config = {};
+            config.enabled = healthBarConfig.value("enabled", config.enabled);
+            config.maxDistance = healthBarConfig.value("maxDistance", config.maxDistance);
+            config.maxDistance = std::max(0.0f, config.maxDistance);
+
+            if (healthBarConfig.contains("colors") && healthBarConfig["colors"].is_object()) {
+                const auto& colors = healthBarConfig["colors"];
+                deserializeColor(colors, "low", config.lowColor);
+                deserializeColor(colors, "mid", config.midColor);
+                deserializeColor(colors, "high", config.highColor);
+                deserializeColor(colors, "border", config.borderColor);
+                deserializeColor(colors, "background", config.backgroundColor);
+                deserializeColor(colors, "highlight", config.highlightColor);
+            }
+        }
+
+        void render(our::World* world, our::Application* app, const our::UIRenderer& ui,
+                    const our::CameraComponent* camera) const {
+            if (!(config.enabled && world && app && camera)) return;
+
+            glm::ivec2 framebufferSize = app->getFrameBufferSize();
+            if (framebufferSize.x <= 0 || framebufferSize.y <= 0) return;
+
+            glm::mat4 view = camera->getViewMatrix();
+            glm::mat4 proj = camera->getProjectionMatrix(framebufferSize);
+            glm::mat4 viewProj = proj * view;
+            glm::mat4 overlayProj = ui.overlayProjection(framebufferSize);
+            glm::vec3 cameraPos = glm::vec3(camera->getOwner()->getLocalToWorldMatrix() * glm::vec4(0, 0, 0, 1));
+
+            for (our::Entity* entity : world->getEntities()) {
+                auto* health = entity->getComponent<HealthComponent>();
+                if (!(entity->getComponent<EnemyComponent>() && health) || health->isDead || health->maxHealth <= 0.0f)
+                    continue;
+
+                float healthRatio = health->getHealthRatio();
+                glm::mat4 localToWorld = entity->getLocalToWorldMatrix();
+                glm::vec3 enemyPosition = glm::vec3(localToWorld * glm::vec4(0, 0, 0, 1));
+                float distance = glm::distance(enemyPosition, cameraPos);
+
+                bool visibleWhenDamaged = health->damageRevealTimer > 0.0f;
+                bool visibleWhenClose = distance <= config.maxDistance;
+
+                if (!(visibleWhenDamaged || visibleWhenClose)) continue;
+
+                ColliderComponent* collider = entity->getComponent<ColliderComponent>();
+                float barHeightOffset = estimateBarHeight(entity, collider) + 0.35f;
+
+                glm::vec3 barWorldPos = glm::vec3(localToWorld * glm::vec4(0.0f, barHeightOffset, 0.0f, 1.0f));
+                our::ScreenPoint screen = our::UIRenderer::worldToScreen(barWorldPos, viewProj, framebufferSize);
+                if (!screen.visible) continue;
+
+                float dist = glm::clamp((distance - 6.0f) / glm::max(1.0f, config.maxDistance - 6.0f), 0.0f, 1.0f);
+                float alpha = visibleWhenDamaged
+                                  ? 1.0f
+                                  : 1.0f - glm::smoothstep(config.maxDistance * 0.7f, config.maxDistance, distance);
+                if (alpha <= 0.0f) continue;
+
+                float barWidth = glm::mix(86.0f, 48.0f, dist);
+                float barHeight = glm::mix(10.0f, 6.0f, dist);
+
+                glm::vec2 barPosition = {screen.position.x - barWidth * 0.5f, screen.position.y - barHeight};
+                glm::vec2 outerSize = {barWidth + 2.0f, barHeight + 2.0f};
+                glm::vec2 innerPosition = barPosition + glm::vec2(2.0f, 2.0f);
+                glm::vec2 innerSize = {barWidth - 4.0f, barHeight - 4.0f};
+                glm::vec2 fillSize = {innerSize.x * healthRatio, innerSize.y};
+
+                glm::vec4 borderColor = config.borderColor;
+                borderColor.a *= alpha;
+                ui.drawRect(overlayProj, barPosition - glm::vec2(1.0f), outerSize, borderColor);
+
+                glm::vec4 backgroundColor = config.backgroundColor;
+                backgroundColor.a *= alpha;
+                ui.drawRect(overlayProj, barPosition, {barWidth, barHeight}, backgroundColor);
+
+                float clampedHealthRatio = glm::clamp(healthRatio, 0.0f, 1.0f);
+                glm::vec4 fillColor =
+                    clampedHealthRatio < 0.5f
+                        ? glm::mix(config.lowColor, config.midColor, clampedHealthRatio * 2.0f)
+                        : glm::mix(config.midColor, config.highColor, (clampedHealthRatio - 0.5f) * 2.0f);
+                fillColor.a *= alpha;
+                ui.drawRect(overlayProj, innerPosition, fillSize, fillColor);
+
+                if (fillSize.x > 6.0f) {
+                    glm::vec4 highlightColor = config.highlightColor;
+                    highlightColor.a *= alpha;
+                    ui.drawRect(overlayProj, innerPosition + glm::vec2(0.0f, 1.0f),
+                                {fillSize.x, std::max(1.0f, innerSize.y * 0.28f)}, highlightColor);
+                }
+            }
+        }
+    };
+
+}  // namespace gameplay