From f791a1d3d5d00b96222bdf87c3c1a80059691cf9 Mon Sep 17 00:00:00 2001
From: a dinosaur <dino@a-dinosaur.com>
Date: Sun, 1 Jun 2025 11:36:15 +1000
Subject: [PATCH] c: Shared random implementation

---
 src/c/lesson9.c | 24 ++++++------------------
 src/c/nehe.c    | 14 ++++++++++++++
 src/c/nehe.h    |  3 +++
 3 files changed, 23 insertions(+), 18 deletions(-)

diff --git a/src/c/lesson9.c b/src/c/lesson9.c
index 0426ce0..082a488 100644
--- a/src/c/lesson9.c
+++ b/src/c/lesson9.c
@@ -55,18 +55,6 @@ static float zoom = -15.0f;
 static float tilt = 90.0f;
 static float spin = 0.0f;
 
-static uint32_t rngState = 1;
-static inline int RngNext(void)
-{
-	//TODO: check which one of these matches win32
-#if 0
-	rngState = rngState * 1103515245 + 12345;
-#else
-	rngState = rngState * 214013 + 2531011;
-#endif
-	return (int)((rngState >> 16) & 0x7FFF);  // (s / 65536) % 32768
-}
-
 
 static bool Lesson9_Init(NeHeContext* ctx)
 {
@@ -192,9 +180,9 @@ static bool Lesson9_Init(NeHeContext* ctx)
 		{
 			.angle = 0.0f,
 			.distance = 5.0f * ((float)i / (float)numStars),
-			.r = (uint8_t)(RngNext() % 256),
-			.g = (uint8_t)(RngNext() % 256),
-			.b = (uint8_t)(RngNext() % 256)
+			.r = (uint8_t)(NeHe_Random() % 256),
+			.g = (uint8_t)(NeHe_Random() % 256),
+			.b = (uint8_t)(NeHe_Random() % 256)
 		};
 	}
 
@@ -270,9 +258,9 @@ static void Lesson9_Draw(NeHeContext* restrict ctx, SDL_GPUCommandBuffer* restri
 		if (star->distance < 0.0f)
 		{
 			star->distance += 5.0f;
-			star->r = (uint8_t)(RngNext() % 256);
-			star->g = (uint8_t)(RngNext() % 256);
-			star->b = (uint8_t)(RngNext() % 256);
+			star->r = (uint8_t)(NeHe_Random() % 256);
+			star->g = (uint8_t)(NeHe_Random() % 256);
+			star->b = (uint8_t)(NeHe_Random() % 256);
 		}
 	}
 	SDL_UnmapGPUTransferBuffer(ctx->device, instanceXferBuffer);
diff --git a/src/c/nehe.c b/src/c/nehe.c
index 620860f..142eb52 100644
--- a/src/c/nehe.c
+++ b/src/c/nehe.c
@@ -6,6 +6,20 @@
 #include "nehe.h"
 
 
+static uint32_t rngState = 1;
+
+int NeHe_Random(void)
+{
+	rngState = rngState * 214013 + 2531011;
+	return (int)((rngState >> 16) & 0x7FFF);  // (s / 65536) % 32768
+}
+
+void NeHe_RandomSeed(uint32_t seed)
+{
+	rngState = seed;
+}
+
+
 bool NeHe_InitGPU(NeHeContext* ctx, const char* title, int width, int height)
 {
 	// Create window
diff --git a/src/c/nehe.h b/src/c/nehe.h
index 2f72ef1..80b8072 100644
--- a/src/c/nehe.h
+++ b/src/c/nehe.h
@@ -26,6 +26,9 @@ typedef struct
 	unsigned fragmentSamplers;
 } NeHeShaderProgramCreateInfo;
 
+int NeHe_Random(void);
+void NeHe_RandomSeed(uint32_t seed);
+
 bool NeHe_InitGPU(NeHeContext* ctx, const char* title, int width, int height);
 bool NeHe_SetupDepthTexture(NeHeContext* ctx, uint32_t width, uint32_t height,
 	SDL_GPUTextureFormat format, float clearDepth);