[example] Added textures_frame_buffer_rendering (#5468)

examples/textures/textures_framebuffer_rendering.c

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+/*******************************************************************************************
+*
+*   raylib [textures] example - framebuffer rendering
+*
+*   Example complexity rating: [★★☆☆] 2/4
+*
+*   Example originally created with raylib 5.6, last time updated with raylib 5.6
+*
+*   Example contributed by Jack Boakes (@jackboakes) 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) 2026-2026 Jack Boakes (@jackboakes)
+*
+********************************************************************************************/
+
+#include "raylib.h"
+#include "raymath.h"
+
+//------------------------------------------------------------------------------------
+// Module Functions Declaration
+//------------------------------------------------------------------------------------
+static void DrawCameraPrism(Camera3D camera, float aspect, Color color);
+
+//------------------------------------------------------------------------------------
+// Program main entry point
+//------------------------------------------------------------------------------------
+int main(void)
+{
+    // Initialization
+    //--------------------------------------------------------------------------------------
+    const int screenWidth = 800;
+    const int screenHeight = 450;
+    const int splitWidth = screenWidth/2;
+
+    InitWindow(screenWidth, screenHeight, "raylib [textures] example - framebuffer rendering");
+
+    // Camera to look at the 3D world
+    Camera3D subjectCamera = { 0 };
+    subjectCamera.position = (Vector3){ 5.0f, 5.0f, 5.0f };
+    subjectCamera.target = (Vector3){ 0.0f, 0.0f, 0.0f };
+    subjectCamera.up = (Vector3){ 0.0f, 1.0f, 0.0f };
+    subjectCamera.fovy = 45.0f;
+    subjectCamera.projection = CAMERA_PERSPECTIVE;
+
+    // Camera to observe the subject camera and 3D world
+    Camera3D observerCamera = { 0 };
+    observerCamera.position = (Vector3){ 10.0f, 10.0f, 10.0f };
+    observerCamera.target = (Vector3){ 0.0f, 0.0f, 0.0f };
+    observerCamera.up = (Vector3){ 0.0f, 1.0f, 0.0f };
+    observerCamera.fovy = 45.0f;
+    observerCamera.projection = CAMERA_PERSPECTIVE;
+
+    // Set up render textures
+    RenderTexture2D observerTarget = LoadRenderTexture(splitWidth, screenHeight);
+    Rectangle observerSource = { 0.0f, 0.0f, (float)observerTarget.texture.width, -(float)observerTarget.texture.height };
+    Rectangle observerDest = { 0.0f, 0.0f, (float)splitWidth, (float)screenHeight };
+
+    RenderTexture2D subjectTarget = LoadRenderTexture(splitWidth, screenHeight);
+    Rectangle subjectSource = { 0.0f, 0.0f, (float)subjectTarget.texture.width, -(float)subjectTarget.texture.height };
+    Rectangle subjectDest = { (float)splitWidth, 0.0f, (float)splitWidth, (float)screenHeight };
+    const float textureAspectRatio = (float)subjectTarget.texture.width/(float)subjectTarget.texture.height;
+
+    // Rectangles for cropping render texture
+    const float captureSize = 128.0f;
+    Rectangle cropSource = { (subjectTarget.texture.width - captureSize)/2.0f, (subjectTarget.texture.height - captureSize)/2.0f, captureSize, -captureSize };
+    Rectangle cropDest = { splitWidth + 20, 20, captureSize, captureSize};
+
+    SetTargetFPS(60);
+    DisableCursor();
+    //--------------------------------------------------------------------------------------
+
+    // Main game loop
+    while (!WindowShouldClose())    // Detect window close button or ESC key
+    {
+        // Update
+        //----------------------------------------------------------------------------------
+        UpdateCamera(&observerCamera, CAMERA_FREE);
+        UpdateCamera(&subjectCamera, CAMERA_ORBITAL);
+
+        if (IsKeyPressed(KEY_R)) observerCamera.target = (Vector3){ 0.0f, 0.0f, 0.0f };
+
+        // Build LHS observer view texture
+        BeginTextureMode(observerTarget);
+
+            ClearBackground(RAYWHITE);
+
+            BeginMode3D(observerCamera);
+
+                DrawGrid(10, 1.0f);
+                DrawCube((Vector3){ 0.0f, 0.0f, 0.0f }, 2.0f, 2.0f, 2.0f, GOLD);
+                DrawCubeWires((Vector3){ 0.0f, 0.0f, 0.0f }, 2.0f, 2.0f, 2.0f, PINK);
+                DrawCameraPrism(subjectCamera, textureAspectRatio, GREEN);
+
+            EndMode3D();
+
+            DrawText("Observer View", 10, observerTarget.texture.height - 30, 20, BLACK);
+            DrawText("WASD + Mouse to Move", 10, 10, 20, DARKGRAY);
+            DrawText("Scroll to Zoom", 10, 30, 20, DARKGRAY);
+            DrawText("R to Reset Observer Target", 10, 50, 20, DARKGRAY);
+
+        EndTextureMode();
+
+        // Build RHS subject view texture
+        BeginTextureMode(subjectTarget);
+
+            ClearBackground(RAYWHITE);
+
+            BeginMode3D(subjectCamera);
+
+                DrawCube((Vector3){ 0.0f, 0.0f, 0.0f }, 2.0f, 2.0f, 2.0f, GOLD);
+                DrawCubeWires((Vector3){ 0.0f, 0.0f, 0.0f }, 2.0f, 2.0f, 2.0f, PINK);
+                DrawGrid(10, 1.0f);
+
+            EndMode3D();
+
+            DrawRectangleLines((subjectTarget.texture.width - captureSize)/2, (subjectTarget.texture.height - captureSize)/2, captureSize, captureSize, GREEN);
+            DrawText("Subject View", 10, subjectTarget.texture.height - 30, 20, BLACK);
+
+        EndTextureMode();
+        //----------------------------------------------------------------------------------
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        BeginDrawing();
+
+            ClearBackground(BLACK);
+
+            // Draw observer texture LHS
+            DrawTexturePro(observerTarget.texture, observerSource, observerDest, (Vector2){0.0f, 0.0f }, 0.0f, WHITE);
+
+            // Draw subject texture RHS
+            DrawTexturePro(subjectTarget.texture, subjectSource, subjectDest, (Vector2){ 0.0f, 0.0f }, 0.0f, WHITE);
+
+            // Draw the small crop overlay on top
+            DrawTexturePro(subjectTarget.texture, cropSource, cropDest, (Vector2){ 0.0f, 0.0f }, 0.0f, WHITE);
+            DrawRectangleLinesEx(cropDest, 2, BLACK);
+
+            // Draw split screen divider line
+            DrawLine(splitWidth, 0, splitWidth, screenHeight, BLACK);
+
+        EndDrawing();
+        //----------------------------------------------------------------------------------
+    }
+
+    // De-Initialization
+    //--------------------------------------------------------------------------------------
+    UnloadRenderTexture(observerTarget);
+    UnloadRenderTexture(subjectTarget);
+    CloseWindow();        // Close window and OpenGL context
+    //--------------------------------------------------------------------------------------
+
+    return 0;
+}
+
+//----------------------------------------------------------------------------------
+// Module Functions Definition
+//----------------------------------------------------------------------------------
+static void DrawCameraPrism(Camera3D camera, float aspect, Color color)
+{
+    float length = Vector3Distance(camera.position, camera.target);
+    // Define the 4 corners of the camera's prism plane sliced at the target in Normalized Device Coordinates
+    Vector3 planeNDC[4] = {
+        { -1.0f, -1.0f, 1.0f }, // Bottom Left
+        {  1.0f, -1.0f, 1.0f }, // Bottom Right
+        {  1.0f,  1.0f, 1.0f }, // Top Right
+        { -1.0f,  1.0f, 1.0f }  // Top Left
+    };
+
+    // Build the matrices
+    Matrix view = GetCameraMatrix(camera);
+    Matrix proj = MatrixPerspective(camera.fovy * DEG2RAD, aspect, 0.05f, length);
+    // Combine view and projection so we can reverse the full camera transform
+    Matrix viewProj = MatrixMultiply(view, proj);
+    // Invert the view-projection matrix to unproject points from NDC space back into world space
+    Matrix inverseViewProj = MatrixInvert(viewProj);
+
+    // Transform the 4 plane corners from NDC into world space
+    Vector3 corners[4];
+    for (int i = 0; i < 4; i++)
+    {
+        float x = planeNDC[i].x;
+        float y = planeNDC[i].y;
+        float z = planeNDC[i].z;
+
+        // Multiply NDC position by the inverse view-projection matrix
+        // This produces a homogeneous (x, y, z, w) position in world space
+        float vx = inverseViewProj.m0*x + inverseViewProj.m4*y + inverseViewProj.m8*z + inverseViewProj.m12;
+        float vy = inverseViewProj.m1*x + inverseViewProj.m5*y + inverseViewProj.m9*z + inverseViewProj.m13;
+        float vz = inverseViewProj.m2*x + inverseViewProj.m6*y + inverseViewProj.m10*z + inverseViewProj.m14;
+        float vw = inverseViewProj.m3*x + inverseViewProj.m7*y + inverseViewProj.m11*z + inverseViewProj.m15;
+
+        corners[i] = (Vector3){ vx/vw, vy/vw, vz/vw };
+    }
+
+    // Draw the far plane sliced at the target
+    DrawLine3D(corners[0], corners[1], color);
+    DrawLine3D(corners[1], corners[2], color);
+    DrawLine3D(corners[2], corners[3], color);
+    DrawLine3D(corners[3], corners[0], color);
+
+    // Draw the prism lines from the far plane to the camera position
+    for (int i = 0; i < 4; i++)
+    {
+        DrawLine3D(camera.position, corners[i], color);
+    }
+}