always pass the parameters and verify that they're correct

include/llmr/geometry/vao.hpp

@@ -3,38 +3,50 @@
 
 #include <llmr/platform/gl.hpp>
 
-#include <cassert>
+#include <stdexcept>
 
 namespace llmr {
 
 class VertexArrayObject {
 public:
     template <typename Shader, typename VertexBuffer>
-    inline void setup(Shader& shader, VertexBuffer& vertex_buffer, char *vertex_offset) {
-        glGenVertexArrays(1, &vao);
-        glBindVertexArray(vao);
+    void bind(Shader& shader, VertexBuffer& vertex_buffer, char *vertex_offset) {
+        if (!vao) {
+            glGenVertexArrays(1, &vao);
+            glBindVertexArray(vao);
 
-        vertex_buffer.bind();
-        shader.bind_vertex(vertex_offset);
+            vertex_buffer.bind();
+            shader.bind_vertex(vertex_offset);
+
+            program = shader.program;
+            buffer = &vertex_buffer;
+            offset = vertex_offset;
+        } else if (program != shader.program) {
+            throw std::runtime_error("trying to bind VAO to different program");
+        } else if (buffer != &vertex_buffer) {
+            throw std::runtime_error("trying to bind VAO to another buffer");
+        } else if (offset != vertex_offset) {
+            throw std::runtime_error("trying to bind VAO to another offset");
+        } else {
+            // This is the correct program for this VAO.
+            glBindVertexArray(vao);
+        }
     }
 
-    inline ~VertexArrayObject() {
+    ~VertexArrayObject() {
         if (vao) {
             glDeleteVertexArrays(1, &vao);
         }
     }
 
-    inline operator bool() const {
-        return vao != 0;
-    }
-
-    inline void bind() {
-        assert(vao);
-        glBindVertexArray(vao);
-    }
-
 private:
     GLuint vao = 0;
+
+    // For debug reasons, we're storing the bind information so that we can
+    // detect errors and report
+    GLuint program = 0;
+    void *buffer = NULL;
+    char *offset = 0;
 };
 
 }

include/llmr/renderer/fill_bucket.hpp

@@ -66,11 +66,7 @@ void FillBucket::drawElements(Shader& shader) {
     char *vertex_index = BUFFER_OFFSET(vertex_start * 2 * sizeof(int16_t));
     char *elements_index = BUFFER_OFFSET(elements_start * 3 * sizeof(int16_t));
     for (group& group : groups) {
-        if (!group.array) {
-            group.array.setup(shader, *buffer, vertex_index);
-        } else {
-            group.array.bind();
-        }
+        group.array.bind(shader, *buffer, vertex_index);
         glDrawElements(GL_TRIANGLES, group.elements_length * 3 - 3, GL_UNSIGNED_SHORT, elements_index);
         vertex_index += group.vertex_length * 2 * sizeof(uint16_t);
         elements_index += group.elements_length * 3 * sizeof(uint16_t);
@@ -80,12 +76,8 @@ void FillBucket::drawElements(Shader& shader) {
 template <typename Shader>
 void FillBucket::drawVertices(Shader& shader) {
     // Draw the entire line
-    if (!array) {
-        char *vertex_index = BUFFER_OFFSET(vertex_start * 2 * sizeof(int16_t));
-        array.setup(shader, *buffer, vertex_index);
-    } else {
-        array.bind();
-    }
+    char *vertex_index = BUFFER_OFFSET(vertex_start * 2 * sizeof(int16_t));
+    array.bind(shader, *buffer, vertex_index);
     glDrawArrays(GL_LINE_STRIP, 0, length);
 }