h-raylib-6.1.0.0: raylib/examples/models/models_procedural_decals.c
/*******************************************************************************************
*
* raylib [models] example - procedural decals
*
* Example demonstrates projecting decals onto a 3D mesh surface by transforming the
* mesh's own triangles into the decal's local space and clipping them against a box,
* using only procedurally generated geometry and textures (no external resource files)
*
* NOTE: This is the same clip-space decal projection idea used by models_decals.c
* (in turn based on three.js' DecalGeometry), applied here to a generated mesh and
* generated textures instead of a loaded model, so the example is fully self-contained
*
* Example complexity rating: [★★★★] 4/4
*
* Example originally created with raylib 6.0, last time updated with raylib 6.0
*
* Example contributed by PanicTitan (@PanicTitan) and reviewed by Ramon Santamaria (@raysan5)
*
* Example licensed under an unmodified zlib/libpng license, which is an OSI-certified,
* BSD-like license that allows static linking with closed source software
*
* Copyright (c) 2025 PanicTitan (@PanicTitan)
*
********************************************************************************************/
#include "raylib.h"
#define RAYGUI_IMPLEMENTATION
#include "raygui.h"
#include "raymath.h"
#include <stddef.h> // Required for: NULL
#include <string.h> // Required for: memcpy()
#include <math.h> // Required for: fabsf(), fminf()
//--------------------------------------------------------------------------------------
// Global Definitions
//--------------------------------------------------------------------------------------
#define MAX_DECALS 256
//--------------------------------------------------------------------------------------
// Types and Structures Definition
//--------------------------------------------------------------------------------------
// Growable triangle-soup buffer used while building a clipped decal mesh
typedef struct MeshBuilder {
int vertexCount;
int vertexCapacity;
Vector3 *vertices;
Vector2 *uvs;
} MeshBuilder;
//------------------------------------------------------------------------------------
// Module Functions Declaration
//------------------------------------------------------------------------------------
static void AddTriangleToMeshBuilder(MeshBuilder *mb, Vector3 v0, Vector3 v1, Vector3 v2);
static void FreeMeshBuilder(MeshBuilder *mb);
static Mesh BuildMesh(MeshBuilder *mb);
static Vector3 ClipSegment(Vector3 v0, Vector3 v1, Vector3 p, float s);
static Mesh GenMeshDecal(Model model, Matrix projection, float decalSize, float decalOffset);
//------------------------------------------------------------------------------------
// Program main entry point
//------------------------------------------------------------------------------------
int main(void)
{
// Initialization
//--------------------------------------------------------------------------------------
const int screenWidth = 800;
const int screenHeight = 450;
SetConfigFlags(FLAG_MSAA_4X_HINT);
InitWindow(screenWidth, screenHeight, "raylib [models] example - procedural decals");
Camera3D camera = { 0 };
camera.position = (Vector3){ 0.0f, 2.5f, 5.0f };
camera.target = (Vector3){ 0.0f, 0.0f, 0.0f };
camera.up = (Vector3){ 0.0f, 1.0f, 0.0f };
camera.fovy = 45.0f;
camera.projection = CAMERA_PERSPECTIVE;
// Target model: a procedurally generated knot with a checkerboard skin
Model model = LoadModelFromMesh(GenMeshTorus(0.8f, 1.8f, 32, 64));
Image checkerImage = GenImageChecked(512, 512, 32, 32, LIGHTGRAY, GRAY);
Texture2D modelTexture = LoadTextureFromImage(checkerImage);
UnloadImage(checkerImage);
SetTextureFilter(modelTexture, TEXTURE_FILTER_BILINEAR);
model.materials[0].maps[MATERIAL_MAP_DIFFUSE].texture = modelTexture;
BoundingBox modelBBox = GetMeshBoundingBox(model.meshes[0]);
camera.target = Vector3Lerp(modelBBox.min, modelBBox.max, 0.5f);
float modelSize = fminf(fminf(fabsf(modelBBox.max.x - modelBBox.min.x),
fabsf(modelBBox.max.y - modelBBox.min.y)), fabsf(modelBBox.max.z - modelBBox.min.z));
float decalSize = modelSize*0.35f;
float decalOffset = 0.01f;
// Translucent cube previewing where the next decal will land
Model placementCube = LoadModelFromMesh(GenMeshCube(decalSize, decalSize, decalSize));
placementCube.materials[0].maps[0].color = LIME;
// Decal texture: a procedurally drawn target/bullseye, no image file needed
Image decalImage = GenImageColor(128, 128, BLANK);
ImageDrawCircle(&decalImage, 64, 64, 60, RED);
ImageDrawCircle(&decalImage, 64, 64, 45, WHITE);
ImageDrawCircle(&decalImage, 64, 64, 30, RED);
ImageDrawCircle(&decalImage, 64, 64, 15, YELLOW);
Texture2D decalTexture = LoadTextureFromImage(decalImage);
UnloadImage(decalImage);
SetTextureFilter(decalTexture, TEXTURE_FILTER_BILINEAR);
Material decalMaterial = LoadMaterialDefault();
decalMaterial.maps[MATERIAL_MAP_DIFFUSE].texture = decalTexture;
decalMaterial.maps[MATERIAL_MAP_DIFFUSE].color = RAYWHITE;
bool showModel = true;
Model decals[MAX_DECALS] = { 0 };
int decalCount = 0;
SetTargetFPS(60);
//--------------------------------------------------------------------------------------
// Main game loop
while (!WindowShouldClose()) // Detect window close button or ESC key
{
// Update
//----------------------------------------------------------------------------------
if (IsMouseButtonDown(MOUSE_BUTTON_RIGHT)) UpdateCamera(&camera, CAMERA_THIRD_PERSON);
// Cast a ray from the mouse and keep the closest point it hits on the model
Ray ray = GetScreenToWorldRay(GetMousePosition(), camera);
RayCollision collision = { 0 };
if (GetRayCollisionBox(ray, modelBBox).hit && (decalCount < MAX_DECALS))
{
for (int m = 0; m < model.meshCount; m++)
{
RayCollision meshHit = GetRayCollisionMesh(ray, model.meshes[m], model.transform);
if (meshHit.hit && (!collision.hit || (meshHit.distance < collision.distance))) collision = meshHit;
}
}
// Project a new decal at the hit point, facing along the surface normal
if (collision.hit && IsMouseButtonPressed(MOUSE_BUTTON_LEFT) && (decalCount < MAX_DECALS))
{
Vector3 lookTarget = Vector3Add(collision.point, collision.normal);
Matrix splat = MatrixLookAt(collision.point, lookTarget, (Vector3){ 0.0f, 1.0f, 0.0f });
splat = MatrixMultiply(splat, MatrixRotateZ(DEG2RAD*(float)GetRandomValue(-180, 180)));
Mesh decalMesh = GenMeshDecal(model, splat, decalSize, decalOffset);
if (decalMesh.vertexCount > 0)
{
decals[decalCount] = LoadModelFromMesh(decalMesh);
decals[decalCount].materials[0].maps[0] = decalMaterial.maps[0];
decalCount++;
}
}
//----------------------------------------------------------------------------------
// Draw
//----------------------------------------------------------------------------------
BeginDrawing();
ClearBackground(RAYWHITE);
BeginMode3D(camera);
if (showModel) DrawModel(model, Vector3Zero(), 1.0f, WHITE);
for (int i = 0; i < decalCount; i++) DrawModel(decals[i], Vector3Zero(), 1.0f, WHITE);
// Preview cube at the surface point currently under the mouse
if (collision.hit)
{
Vector3 lookTarget = Vector3Add(collision.point, collision.normal);
Matrix splat = MatrixLookAt(collision.point, lookTarget, (Vector3){ 0.0f, 1.0f, 0.0f });
placementCube.transform = MatrixInvert(splat);
DrawModel(placementCube, Vector3Zero(), 1.0f, Fade(WHITE, 0.5f));
}
DrawGrid(10, 1.0f);
EndMode3D();
// Vertex/triangle counts: base model vs total once decal geometry is added
int baseVertices = 0, baseTriangles = 0;
for (int i = 0; i < model.meshCount; i++)
{
baseVertices += model.meshes[i].vertexCount;
baseTriangles += model.meshes[i].triangleCount;
}
int totalVertices = baseVertices, totalTriangles = baseTriangles;
for (int i = 0; i < decalCount; i++)
{
totalVertices += decals[i].meshes[0].vertexCount;
totalTriangles += decals[i].meshes[0].triangleCount;
}
int statX = screenWidth - 280;
DrawText("Vertices", statX + 90, 10, 10, LIME);
DrawText("Triangles", statX + 180, 10, 10, LIME);
DrawText("Base Model", statX, 25, 10, LIME);
DrawText(TextFormat("%d", baseVertices), statX + 90, 25, 10, LIME);
DrawText(TextFormat("%d", baseTriangles), statX + 180, 25, 10, LIME);
DrawText("TOTAL", statX, 40, 10, LIME);
DrawText(TextFormat("%d", totalVertices), statX + 90, 40, 10, LIME);
DrawText(TextFormat("%d", totalTriangles), statX + 180, 40, 10, LIME);
if (GuiButton((Rectangle){ 10, screenHeight - 80.0f, 100, 40 }, showModel ? "Hide Model" : "Show Model"))
showModel = !showModel;
if (GuiButton((Rectangle){ 120, screenHeight - 80.0f, 100, 40 }, "Clear Decals"))
{
for (int i = 0; i < decalCount; i++) UnloadModel(decals[i]);
decalCount = 0;
}
DrawText("Left click: place decal | Right drag: orbit camera", 10, screenHeight - 25, 10, DARKGRAY);
DrawFPS(10, 10);
EndDrawing();
//----------------------------------------------------------------------------------
}
// De-Initialization
//--------------------------------------------------------------------------------------
for (int i = 0; i < decalCount; i++) UnloadModel(decals[i]);
UnloadModel(placementCube);
UnloadTexture(decalTexture);
UnloadTexture(modelTexture);
UnloadModel(model);
CloseWindow(); // Close window and OpenGL context
//--------------------------------------------------------------------------------------
return 0;
}
//----------------------------------------------------------------------------------
// Module Functions Definition
//----------------------------------------------------------------------------------
// Appends a triangle to a growable mesh builder buffer, growing it in fixed-size chunks
static void AddTriangleToMeshBuilder(MeshBuilder *mb, Vector3 v0, Vector3 v1, Vector3 v2)
{
if (mb->vertexCapacity <= (mb->vertexCount + 3))
{
int newVertexCapacity = (1 + (mb->vertexCapacity/256))*256;
Vector3 *newVertices = (Vector3 *)MemAlloc(newVertexCapacity*sizeof(Vector3));
if (mb->vertexCapacity > 0)
{
memcpy(newVertices, mb->vertices, mb->vertexCount*sizeof(Vector3));
MemFree(mb->vertices);
}
mb->vertices = newVertices;
mb->vertexCapacity = newVertexCapacity;
}
int index = mb->vertexCount;
mb->vertexCount += 3;
mb->vertices[index + 0] = v0;
mb->vertices[index + 1] = v1;
mb->vertices[index + 2] = v2;
}
// Frees a mesh builder's backing buffers
static void FreeMeshBuilder(MeshBuilder *mb)
{
if (mb->vertices != NULL) MemFree(mb->vertices);
if (mb->uvs != NULL) MemFree(mb->uvs);
*mb = (MeshBuilder){ 0 };
}
// Converts a mesh builder's triangle soup into a standard uploaded raylib Mesh
static Mesh BuildMesh(MeshBuilder *mb)
{
Mesh outMesh = { 0 };
outMesh.vertexCount = mb->vertexCount;
outMesh.triangleCount = mb->vertexCount/3;
outMesh.vertices = (float *)MemAlloc(outMesh.vertexCount*3*sizeof(float));
if (mb->uvs != NULL) outMesh.texcoords = (float *)MemAlloc(outMesh.vertexCount*2*sizeof(float));
for (int i = 0; i < mb->vertexCount; i++)
{
outMesh.vertices[3*i + 0] = mb->vertices[i].x;
outMesh.vertices[3*i + 1] = mb->vertices[i].y;
outMesh.vertices[3*i + 2] = mb->vertices[i].z;
if (mb->uvs != NULL)
{
outMesh.texcoords[2*i + 0] = mb->uvs[i].x;
outMesh.texcoords[2*i + 1] = mb->uvs[i].y;
}
}
UploadMesh(&outMesh, false);
return outMesh;
}
// Clips the segment [v0, v1] against the plane p.x = s, returning the intersection point
static Vector3 ClipSegment(Vector3 v0, Vector3 v1, Vector3 p, float s)
{
float d0 = Vector3DotProduct(v0, p) - s;
float d1 = Vector3DotProduct(v1, p) - s;
float t = d0/(d0 - d1);
return Vector3Lerp(v0, v1, t);
}
// Builds a decal mesh: the model's triangles are transformed into the decal's local space
// (so the decal sits at the origin, facing +Z) and clipped against a decalSize-sided box,
// following the same clip-space projection idea used by engines' decal systems (and by
// three.js' DecalGeometry, which the technique is commonly traced back to). What's left
// after clipping becomes the decal's own small mesh, UV-mapped from its local coordinates
static Mesh GenMeshDecal(Model model, Matrix projection, float decalSize, float decalOffset)
{
Matrix invProj = MatrixInvert(projection);
MeshBuilder meshBuilders[2] = { 0 };
int mbIndex = 0;
// Gather triangles that land anywhere near the decal box; this is a loose, cheap
// pre-filter meant to skip most of the model, the precise clip happens below
for (int meshIndex = 0; meshIndex < model.meshCount; meshIndex++)
{
Mesh mesh = model.meshes[meshIndex];
for (int tri = 0; tri < mesh.triangleCount; tri++)
{
Vector3 vertices[3] = { 0 };
if (mesh.indices == NULL)
{
for (int v = 0; v < 3; v++)
{
vertices[v] = (Vector3){
mesh.vertices[3*3*tri + 3*v + 0],
mesh.vertices[3*3*tri + 3*v + 1],
mesh.vertices[3*3*tri + 3*v + 2]
};
}
}
else
{
for (int v = 0; v < 3; v++)
{
int idx = mesh.indices[3*tri + v];
vertices[v] = (Vector3){
mesh.vertices[3*idx + 0],
mesh.vertices[3*idx + 1],
mesh.vertices[3*idx + 2]
};
}
}
int insideCount = 0;
for (int i = 0; i < 3; i++)
{
Vector3 v = Vector3Transform(vertices[i], projection);
if ((fabsf(v.x) < decalSize) || (fabsf(v.y) <= decalSize) || (fabsf(v.z) <= decalSize)) insideCount++;
vertices[i] = v;
}
if (insideCount > 0) AddTriangleToMeshBuilder(&meshBuilders[mbIndex], vertices[0], vertices[1], vertices[2]);
}
}
// Clip the surviving triangles against each of the decal box's 6 faces in turn
Vector3 planes[6] = {
{ 1, 0, 0 }, { -1, 0, 0 },
{ 0, 1, 0 }, { 0, -1, 0 },
{ 0, 0, 1 }, { 0, 0, -1 }
};
for (int face = 0; face < 6; face++)
{
mbIndex = 1 - mbIndex;
MeshBuilder *inMesh = &meshBuilders[1 - mbIndex];
MeshBuilder *outMesh = &meshBuilders[mbIndex];
outMesh->vertexCount = 0;
float s = 0.5f*decalSize;
for (int i = 0; i < inMesh->vertexCount; i += 3)
{
Vector3 nV1, nV2, nV3, nV4;
float d1 = Vector3DotProduct(inMesh->vertices[i + 0], planes[face]) - s;
float d2 = Vector3DotProduct(inMesh->vertices[i + 1], planes[face]) - s;
float d3 = Vector3DotProduct(inMesh->vertices[i + 2], planes[face]) - s;
int v1Out = (d1 > 0);
int v2Out = (d2 > 0);
int v3Out = (d3 > 0);
int total = v1Out + v2Out + v3Out;
switch (total)
{
case 0:
// Whole triangle is inside this face, keep it as-is
AddTriangleToMeshBuilder(outMesh, inMesh->vertices[i], inMesh->vertices[i + 1], inMesh->vertices[i + 2]);
break;
case 1:
// One corner is outside; clip it off, turning the triangle into a quad
if (v1Out)
{
nV1 = inMesh->vertices[i + 1];
nV2 = inMesh->vertices[i + 2];
nV3 = ClipSegment(inMesh->vertices[i], nV1, planes[face], s);
nV4 = ClipSegment(inMesh->vertices[i], nV2, planes[face], s);
}
if (v2Out)
{
nV1 = inMesh->vertices[i];
nV2 = inMesh->vertices[i + 2];
nV3 = ClipSegment(inMesh->vertices[i + 1], nV1, planes[face], s);
nV4 = ClipSegment(inMesh->vertices[i + 1], nV2, planes[face], s);
AddTriangleToMeshBuilder(outMesh, nV3, nV2, nV1);
AddTriangleToMeshBuilder(outMesh, nV2, nV3, nV4);
break;
}
if (v3Out)
{
nV1 = inMesh->vertices[i];
nV2 = inMesh->vertices[i + 1];
nV3 = ClipSegment(inMesh->vertices[i + 2], nV1, planes[face], s);
nV4 = ClipSegment(inMesh->vertices[i + 2], nV2, planes[face], s);
}
AddTriangleToMeshBuilder(outMesh, nV1, nV2, nV3);
AddTriangleToMeshBuilder(outMesh, nV4, nV3, nV2);
break;
case 2:
// Two corners are outside; only the small corner near the surviving vertex remains
if (!v1Out)
{
nV1 = inMesh->vertices[i];
nV2 = ClipSegment(nV1, inMesh->vertices[i + 1], planes[face], s);
nV3 = ClipSegment(nV1, inMesh->vertices[i + 2], planes[face], s);
AddTriangleToMeshBuilder(outMesh, nV1, nV2, nV3);
}
if (!v2Out)
{
nV1 = inMesh->vertices[i + 1];
nV2 = ClipSegment(nV1, inMesh->vertices[i + 2], planes[face], s);
nV3 = ClipSegment(nV1, inMesh->vertices[i], planes[face], s);
AddTriangleToMeshBuilder(outMesh, nV1, nV2, nV3);
}
if (!v3Out)
{
nV1 = inMesh->vertices[i + 2];
nV2 = ClipSegment(nV1, inMesh->vertices[i], planes[face], s);
nV3 = ClipSegment(nV1, inMesh->vertices[i + 1], planes[face], s);
AddTriangleToMeshBuilder(outMesh, nV1, nV2, nV3);
}
break;
default:
// All 3 corners are outside this face, the triangle is fully clipped away
break;
}
}
}
MeshBuilder *finalMesh = &meshBuilders[mbIndex];
Mesh decalMesh = { 0 };
if (finalMesh->vertexCount > 0)
{
finalMesh->uvs = (Vector2 *)MemAlloc(sizeof(Vector2)*finalMesh->vertexCount);
for (int i = 0; i < finalMesh->vertexCount; i++)
{
// Clipped coordinates run roughly (-decalSize/2 .. decalSize/2); remap to (0..1)
finalMesh->uvs[i].x = (finalMesh->vertices[i].x/decalSize + 0.5f);
finalMesh->uvs[i].y = (finalMesh->vertices[i].y/decalSize + 0.5f);
// Nudge slightly along the normal so the decal doesn't z-fight with the surface
finalMesh->vertices[i].z -= decalOffset;
finalMesh->vertices[i] = Vector3Transform(finalMesh->vertices[i], invProj);
}
decalMesh = BuildMesh(finalMesh);
}
FreeMeshBuilder(&meshBuilders[0]);
FreeMeshBuilder(&meshBuilders[1]);
return decalMesh;
}