add getFreeUBO helper function

src/shader.cpp

@@ -159,6 +159,16 @@ getShaderByID(GLContext* gl_ctx, GLuint prog_id)
 	return nullptr;
 }
 
+GLBuffer*
+getFreeUBO(GLContext* gl_ctx)
+{
+	if (gl_ctx->num_ubos < gl_ctx->max_ubos)
+		return  &gl_ctx->uniform_buffers[gl_ctx->num_ubos++];
+
+	LOGF(Error, "no free Uniform Buffer Objects\n");
+	return nullptr;
+}
+
 GLTexture*
 getGLTexture(GLContext* gl_ctx, Texture* diffuse_img)
 {

src/shader.h

@@ -186,6 +186,8 @@ ShaderProgram* getShaderByHash(GLContext* gl_ctx, u64 hash);
 
 ShaderProgram* getFreeShader(GLContext* gl_ctx);
 
+GLBuffer* getFreeUBO(GLContext* gl_ctx);
+
 GLTexture* getGLTexture(GLContext* gl_ctx, Texture* diffuse_img);
 
 void renderVAO(GLMesh* glmesh,