Mörsergranate: impact marker on the ground until the explosion

The landing point is noted from the grenade's cEventFX 0x96 at launch; a
translucent red circle with the explosion radius (shared ImpactRadius) is
drawn after the world's ground, under the objects, and ends when that
grenade's impact gathers its targets. Ground -> screen projection in
game/engine/worldview.h.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/dwarf-arts.md

@@ -46,3 +46,27 @@
 - The impact's gather call gets a radius of size × (1 + 0.1 × (level / 5)),
   with the owner's Mörsergranate level (`game::ArtLevel`). The growth 0.1 per
   step is our choice; not yet seen in the game (Borf's level is 2).
+
+## Mörsergranate impact marker (asked 2026-10-25, done 2026-10-26)
+
+"Show exactly where the grenade will land and its explosion radius, a red
+circle with low alpha on the ground."
+
+Measured:
+- The landing point is decided at launch (`0x5145d0` case 0x43e): the
+  target's position, or, closer than 200, a point 200 from the dwarf with a
+  +-15 jitter. It goes to the new grenade (type 0x3fa) in cEventFX 0x96,
+  constructed at `0x5169fa` (`cEventFX::Construct` 0x41e0a0, thiscall, ret
+  0x44: code, owner id, target id, position area / x / y / level, ...).
+- The impact gathers its targets at exactly that point, on several frames.
+  The grenade object stays about 30 s after the explosion.
+- Ground -> screen: `0x622700` (world units -> world pixels, the isometric
+  plane), then (pixel - camera +0x14/+0x18) / zoom +0xb60 + screen centre
+  (floating texts 0x41e546). Checked with the hero: the screen centre.
+- The world view draws the ground (`0x62d530`, ground quad list), then the
+  objects.
+
+Mod: the construct call notes grenade, owner, landing point and radius
+(`ImpactRadius`, shared with the hit check); after `0x62d530` a disc (alpha
+0x40) with a 2 px rim (alpha 0xa0) is drawn there, without depth test, until
+the impact of that owner's grenade at that point gathers its targets.

docs/todo.md

@@ -42,15 +42,6 @@ Known so far: the periodic-hit aura (effect kind 0x12) uses
 mapped yet. Other arts' ranges are not mapped. Fits the data-driven arts
 item above (range as a property of an art, one place to compute it).
 
-Mörsergranate impact indicator (asked 2026-10-25, while reworking the dwarf's
-Kanonenschuss / Mörsergranate): show exactly where the grenade will land and
-its explosion radius, a red circle with low alpha on the ground. The landing
-point seems to be decided at launch (cCreature combat move code `0x5145d0`,
-case 0x43e: the target point, changed by a random offset when closer than
-200; passed as the position of the grenade's cEventFX 0x96), so the circle
-could be drawn from the launch until the explosion; to be confirmed with the
-diagnostic log. To be built after the radius-per-level change.
-
 ## Rename life leech to "omnivamp"
 
 Asked 2026-10-15: life leech (property 0x349, "Lebensentzug") becomes

src/game/engine/worldview.h

@@ -0,0 +1,48 @@
+#pragma once
+// The world view (cWorldView0, vtable 0x8900f8): camera and the projection of
+// world positions onto the screen. docs/widescreen.md.
+
+#include <cstdint>
+
+#include "game/addresses.h"
+#include "game/render/dx_driver7.h"
+
+namespace game {
+
+constexpr size_t kViewCameraX = 0x14;  // int32, world pixels
+constexpr size_t kViewCameraY = 0x18;
+constexpr size_t kViewZoom = 0xb60;    // float, 0.5 .. 2.0
+constexpr float kViewHalfHeight = 384.0f;  // the render height stays 768
+
+struct Point2 {
+    float x, y;
+};
+
+// World units -> world pixels: the ground plane's isometric projection
+// (0x622700, cdecl (out, in), plain ret; matrix at 0xad5710; a 53.66563-unit
+// tile is a 96x48 pixel diamond). The large map uses it too.
+inline Point2 WorldToPlane(float x, float y) {
+    float in[3] = {x, y, 0};
+    float out[3] = {};
+    using Fn = void(__cdecl*)(float*, const float*);
+    reinterpret_cast<Fn>(0x00622700)(out, in);
+    return {out[0], out[1]};
+}
+
+// World pixels -> screen: (pixel - camera) / zoom + screen centre (the
+// floating texts 0x41e546, the object passes 0x62f925). `halfWidth`: half
+// the render width (the centre the widescreen mod gives the view).
+inline Point2 PlaneToScreen(const uint8_t* view, const Point2& plane, float halfWidth) {
+    const float zoom = *reinterpret_cast<const float*>(view + kViewZoom);
+    const auto cameraX = static_cast<float>(*reinterpret_cast<const int32_t*>(view + kViewCameraX));
+    const auto cameraY = static_cast<float>(*reinterpret_cast<const int32_t*>(view + kViewCameraY));
+    return {(plane.x - cameraX) / zoom + halfWidth, (plane.y - cameraY) / zoom + kViewHalfHeight};
+}
+
+// The Direct3D 7 device the world is drawn with.
+inline void* RenderDevice() {
+    const auto* driver = *reinterpret_cast<DxDriver7* const*>(addr::g_dxDriver);
+    return driver ? driver->device : nullptr;
+}
+
+} // namespace game

src/mods/dwarfarts.cpp

@@ -24,16 +24,32 @@
 // plus the creature type's size (object type table 0x428bb0). The mod passes
 // that call a radius of size × (1 + kRadiusGrowth × (level / 5)), with the
 // level of the owner's Mörsergranate.
+//
+// Impact marker (asked 2026-10-25): where the grenade will land and its
+// explosion radius, a red circle with low alpha on the ground. The landing
+// point is decided at launch (0x5145d0 case 0x43e: the target's position, or
+// 200 units from the dwarf with +-15 jitter when closer) and sent to the new
+// grenade with cEventFX 0x96 (constructed at 0x5169fa: code, owner, 0,
+// position area / x / y / level). The construct call notes the grenade and
+// the point; the circle is drawn after the world view's ground (0x62d530,
+// before the objects) until the impact gathers its targets (the grenade
+// object itself stays about 30 s longer).
 
 #include <windows.h>
 
 #include <cstdint>
 #include <cstring>
+#include <algorithm>
+#include <cmath>
 #include <map>
+#include <vector>
 
 #include "game/engine/arts.h"
 #include "game/engine/objects.h"
 #include "game/engine/orders.h"
+#include "game/engine/worldview.h"
+#include "game/ui/draw.h"
+#include "mods/widescreen.h"
 #include "re/hook.h"
 #include "re/log.h"
 #include "re/patch.h"
@@ -42,6 +58,7 @@ namespace mods::dwarfarts {
 
 uint32_t* __fastcall GatherTargets(void* manager, void*, uint32_t* out, const void* position, uint32_t type,
                                    uint32_t only, int32_t radius, const uint8_t* fx);
+void DrawMarkers(const uint8_t* view);
 
 namespace {
 
@@ -81,6 +98,14 @@ int32_t TypeSize(uint32_t type) {
     return reinterpret_cast<Fn>(0x00428bb0)(*reinterpret_cast<void**>(0x00aa9564), nullptr, type);
 }
 
+// The explosion radius of a grenade thrown by `owner` (world units; a
+// creature is hit when within it plus its own size).
+int32_t ImpactRadius(void* owner) {
+    const unsigned level = owner ? game::ArtLevel(owner, game::kArtMoerser) : 0;
+    const int32_t size = TypeSize(kGrenadeImpactType);
+    return static_cast<int32_t>(static_cast<float>(size) * (1.0f + kRadiusGrowth * (level / kLevelsPerStep)));
+}
+
 // 0x5ab400 calls 0x5ff820 (thiscall (out, position, type, only, radius),
 // ret 0x14) with the effect object in ebx.
 __declspec(naked) void GatherTargetsThunk() {
@@ -168,6 +193,151 @@ __declspec(naked) void CreateImpactThunk() {
     }
 }
 
+// --- impact marker ---------------------------------------------------------
+
+constexpr uint32_t kGrenadeEventConstruct = 0x005169fa;  // call cEventFX::Construct
+constexpr uint32_t kFxEventConstruct = 0x0041e0a0;       // thiscall, ret 0x44
+constexpr uint32_t kFxEventLand = 0x96;
+constexpr size_t kObjectId = 0xc;
+constexpr uint32_t kMarkerFill = 0x40ff0000;  // red, low alpha
+constexpr uint32_t kMarkerRim = 0xa0ff2020;
+constexpr float kRimWidth = 2.0f;  // screen pixels
+constexpr int kCircleSegments = 48;
+
+// A grenade object outlives its explosion by about 30 s (measured
+// 2026-10-26), so its marker ends with the explosion: the impact gathering
+// its targets (GatherTargets; it does so on several frames, at exactly the
+// noted landing point).
+constexpr float kImpactMatchDistance = 100.0f;  // world units; the landing jitter is +-15
+
+struct Grenade {
+    uint8_t* object;
+    uint32_t id;
+    uint32_t owner;
+    float x, y;  // landing point, world units
+    float radius;
+};
+std::vector<Grenade> g_grenades;
+
+// The explosion of `owner`'s grenade at `position` (world units): ends the
+// marker of that grenade, the owner's one closest to it.
+void OnImpact(uint32_t owner, float x, float y) {
+    auto closest = g_grenades.end();
+    float best = kImpactMatchDistance;
+    for (auto it = g_grenades.begin(); it != g_grenades.end(); ++it) {
+        const float distance = std::hypot(it->x - x, it->y - y);
+        if (it->owner == owner && distance < best) {
+            best = distance;
+            closest = it;
+        }
+    }
+    if (closest != g_grenades.end()) {
+        g_grenades.erase(closest);
+    }
+}
+
+// Construct's arguments: code, owner id, target id, position (area, x, y,
+// level), ...; the new grenade object is in esi.
+void __cdecl NoteGrenade(const uint32_t* args, uint8_t* grenade) {
+    if (args[0] != kFxEventLand || !grenade) {
+        return;
+    }
+    const auto x = static_cast<float>(static_cast<int32_t>(args[4]));
+    const auto y = static_cast<float>(static_cast<int32_t>(args[5]));
+    const auto radius = static_cast<float>(ImpactRadius(game::GetCreature(args[1])));
+    g_grenades.push_back({grenade, *reinterpret_cast<uint32_t*>(grenade + kObjectId), args[1], x, y, radius});
+}
+
+__declspec(naked) void GrenadeEventThunk() {
+    __asm {
+        pushad
+        lea eax, [esp+24h]  // the arguments (above pushad and the return address)
+        push esi            // the grenade
+        push eax
+        call NoteGrenade
+        add esp, 8
+        popad
+        mov eax, kFxEventConstruct
+        jmp eax
+    }
+}
+
+bool Alive(const Grenade& grenade) {
+    return game::GetObjectById(grenade.id) == grenade.object;
+}
+
+using SetRenderStateFn = HRESULT(__stdcall*)(void*, DWORD, DWORD);
+using GetRenderStateFn = HRESULT(__stdcall*)(void*, DWORD, DWORD*);
+
+// Render states for a translucent overlay without depth, restored after.
+class OverlayStates {
+public:
+    explicit OverlayStates(void* device) : device_(device) {
+        void** vtable = *static_cast<void***>(device);
+        set_ = reinterpret_cast<SetRenderStateFn>(vtable[game::kDeviceSetRenderState]);
+        const auto get = reinterpret_cast<GetRenderStateFn>(vtable[game::kDeviceGetRenderState]);
+        for (size_t i = 0; i < kCount; ++i) {
+            get(device_, kStates[i], &saved_[i]);
+            set_(device_, kStates[i], kValues[i]);
+        }
+    }
+    ~OverlayStates() {
+        for (size_t i = 0; i < kCount; ++i) {
+            set_(device_, kStates[i], saved_[i]);
+        }
+    }
+    OverlayStates(const OverlayStates&) = delete;
+    OverlayStates& operator=(const OverlayStates&) = delete;
+
+private:
+    // D3DRENDERSTATE ZENABLE, ZWRITEENABLE off; alpha blending SRCALPHA /
+    // INVSRCALPHA.
+    static constexpr size_t kCount = 5;
+    static constexpr DWORD kStates[kCount] = {7, 14, game::kStateAlphaBlendEnable, game::kStateSourceBlend,
+                                              game::kStateDestinationBlend};
+    static constexpr DWORD kValues[kCount] = {FALSE, FALSE, TRUE, 5, 6};
+    void* device_;
+    SetRenderStateFn set_ = nullptr;
+    DWORD saved_[kCount] = {};
+};
+
+game::ScreenVertex Vertex(const game::Point2& p, uint32_t colour) {
+    return {p.x, p.y, 0, 1, colour, 0, 0, 0};
+}
+
+// The circle on the ground: a translucent disc and a brighter rim.
+void DrawMarker(const uint8_t* view, void* device, const Grenade& grenade) {
+    const float halfWidth = static_cast<float>(mods::widescreen::RenderWidth()) / 2;
+    const auto screen = [&](float x, float y) {
+        return game::PlaneToScreen(view, game::WorldToPlane(x, y), halfWidth);
+    };
+    const game::Point2 centre = screen(grenade.x, grenade.y);
+    game::Point2 rim[kCircleSegments + 1];
+    for (int i = 0; i <= kCircleSegments; ++i) {
+        const float angle = 6.2831853f * static_cast<float>(i % kCircleSegments) / kCircleSegments;
+        rim[i] = screen(grenade.x + grenade.radius * std::cos(angle), grenade.y + grenade.radius * std::sin(angle));
+    }
+    // The rim band reaches inwards from the circle by kRimWidth.
+    const auto inner = [&](const game::Point2& p) {
+        const float dx = centre.x - p.x, dy = centre.y - p.y;
+        const float length = std::hypot(dx, dy);
+        return length > kRimWidth ? game::Point2{p.x + dx / length * kRimWidth, p.y + dy / length * kRimWidth}
+                                  : centre;
+    };
+    static std::vector<game::ScreenVertex> vertices;
+    vertices.clear();
+    for (int i = 0; i < kCircleSegments; ++i) {
+        vertices.insert(vertices.end(),
+                        {Vertex(centre, kMarkerFill), Vertex(rim[i], kMarkerFill), Vertex(rim[i + 1], kMarkerFill)});
+    }
+    for (int i = 0; i < kCircleSegments; ++i) {
+        const game::Point2 a = rim[i], b = rim[i + 1], c = inner(rim[i]), d = inner(rim[i + 1]);
+        vertices.insert(vertices.end(), {Vertex(a, kMarkerRim), Vertex(b, kMarkerRim), Vertex(c, kMarkerRim),
+                                         Vertex(c, kMarkerRim), Vertex(b, kMarkerRim), Vertex(d, kMarkerRim)});
+    }
+    game::FillTriangles(device, vertices.data(), vertices.size());
+}
+
 void Startup() {
     const bool impact = re::RedirectCall(kImpactCreate, kCreateAt, reinterpret_cast<const void*>(&CreateImpactThunk));
     re::Log("dwarfarts: Kanonenschuss impact only on stuns%s", impact ? "" : " (patch FAILED)");
@@ -185,6 +355,9 @@ void Startup() {
     const bool radius =
         re::RedirectCall(kImpactGatherCall, kGatherInRange, reinterpret_cast<const void*>(&GatherTargetsThunk));
     re::Log("dwarfarts: Mörsergranate radius%s", radius ? "" : " (patch FAILED)");
+    const bool marker = re::RedirectCall(kGrenadeEventConstruct, kFxEventConstruct,
+                                         reinterpret_cast<const void*>(&GrenadeEventThunk));
+    re::Log("dwarfarts: Mörsergranate impact marker%s", marker ? "" : " (patch FAILED)");
 }
 RE_STARTUP(DwarfArtsStartup, Startup);
 
@@ -197,13 +370,44 @@ struct Registration {
 uint32_t* __fastcall GatherTargets(void* manager, void*, uint32_t* out, const void* position, uint32_t type,
                                    uint32_t only, int32_t radius, const uint8_t* fx) {
     if (type == kGrenadeImpactType && radius < 0 && fx) {
-        void* owner = game::GetCreature(*reinterpret_cast<const uint32_t*>(fx + kFxOwner));
+        const uint32_t owner = *reinterpret_cast<const uint32_t*>(fx + kFxOwner);
-        const unsigned level = owner ? game::ArtLevel(owner, game::kArtMoerser) : 0;
+        radius = ImpactRadius(game::GetCreature(owner));
-        const int32_t size = TypeSize(type);
+        // The position: area (u16), x, y (int32, world units), level.
-        radius = static_cast<int32_t>(static_cast<float>(size) * (1.0f + kRadiusGrowth * (level / kLevelsPerStep)));
+        const auto* at = static_cast<const uint8_t*>(position);
+        OnImpact(owner, static_cast<float>(*reinterpret_cast<const int32_t*>(at + 4)),
+                 static_cast<float>(*reinterpret_cast<const int32_t*>(at + 8)));
     }
     using Fn = uint32_t*(__fastcall*)(void*, void*, uint32_t*, const void*, uint32_t, uint32_t, int32_t);
     return reinterpret_cast<Fn>(kGatherInRange)(manager, nullptr, out, position, type, only, radius);
 }
 
+// The impact markers of the grenades in flight, on the ground of `view`.
+void DrawMarkers(const uint8_t* view) {
+    g_grenades.erase(std::remove_if(g_grenades.begin(), g_grenades.end(), [](const Grenade& g) { return !Alive(g); }),
+                     g_grenades.end());
+    void* device = game::RenderDevice();
+    if (g_grenades.empty() || !device) {
+        return;
+    }
+    OverlayStates states(device);
+    for (const Grenade& grenade : g_grenades) {
+        DrawMarker(view, device, grenade);
+    }
+}
+
 } // namespace mods::dwarfarts
+
+namespace game {
+
+// cWorldView0::DrawGroundQuads (0x62d530, thiscall (renderer), ret 4): the
+// ground; the objects are drawn after it.
+void __fastcall WorldView_DrawGroundQuads(uint8_t* self, void* edx, void* renderer);
+RE_HOOK(0x0062d530, WorldView_DrawGroundQuads);
+void __fastcall WorldView_DrawGroundQuads(uint8_t* self, void* edx, void* renderer) {
+    WorldView_DrawGroundQuads_original(self, edx, renderer);
+    if (self) {
+        mods::dwarfarts::DrawMarkers(self);
+    }
+}
+
+} // namespace game

tools/names.txt

@@ -437,3 +437,6 @@
 0x006336b0 World_VisitedBorderCell           # thiscall (cx, cy), ret 8: border byte, 0 outside 100x100
 0x006c8580 cUI_Megamap::DrawVisitedBorder    # thiscall (device), ret 4: 2x2 px red (0xffff0000) dot per border bit, +-10/+-20 px from the sector origin
 0x006c87c0 cUI_Megamap::DrawQuestMarkers     # thiscall (device), ret 4: quest book entries (0xaaaf00)
+0x00622700 WorldToPlane                      # cdecl (out vec3, in vec3), plain ret: world units -> world pixels (iso matrix 0xad5710)
+0x0062d530 cWorldView0::DrawGroundQuads      # thiscall (renderer), ret 4: the ground, before the objects
+0x0041e0a0 cEventFX::Construct               # thiscall (code, owner, target, position 4 dwords, ...), ret 0x44