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Orphan vertex buffers for improved performance

Bump my Raspberry Pi 3B+ from 100FPS to 120FPS.

--- a/src/Backends/Rendering/OpenGL3.cpp

+++ b/src/Backends/Rendering/OpenGL3.cpp

@@ -18,8 +18,6 @@

 #define MIN(a,b) ((a) < (b) ? (a) : (b))

 #define MAX(a,b) ((a) > (b) ? (a) : (b))

-#define TOTAL_VBOS 8

-

 #define ATTRIBUTE_INPUT_VERTEX_COORDINATES 1

 #define ATTRIBUTE_INPUT_TEXTURE_COORDINATES 2

@@ -108,7 +106,7 @@

 #ifndef USE_OPENGLES2

 static GLuint vertex_array_id;

 #endif

-static GLuint vertex_buffer_ids[TOTAL_VBOS];

+static GLuint vertex_buffer_id;

 static GLuint framebuffer_id;

 static VertexBufferSlot *local_vertex_buffer;

@@ -395,31 +393,11 @@

 static void FlushVertexBuffer(void)

 {

-	static size_t vertex_buffer_size[TOTAL_VBOS];

-	static size_t current_vertex_buffer = 0;

-

 	if (current_vertex_buffer_slot == 0)

 		return;

-	// Select new VBO

-	glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_ids[current_vertex_buffer]);

-	glVertexAttribPointer(ATTRIBUTE_INPUT_VERTEX_COORDINATES, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*)offsetof(Vertex, position));

-	glVertexAttribPointer(ATTRIBUTE_INPUT_TEXTURE_COORDINATES, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*)offsetof(Vertex, texture));

+	glBufferData(GL_ARRAY_BUFFER, current_vertex_buffer_slot * sizeof(VertexBufferSlot), local_vertex_buffer, GL_STREAM_DRAW);

-	// Upload vertex buffer to VBO, growing it if necessary

-	if (local_vertex_buffer_size > vertex_buffer_size[current_vertex_buffer])

-	{

-		vertex_buffer_size[current_vertex_buffer] = local_vertex_buffer_size;

-		glBufferData(GL_ARRAY_BUFFER, vertex_buffer_size[current_vertex_buffer] * sizeof(VertexBufferSlot), local_vertex_buffer, GL_DYNAMIC_DRAW);

-	}

-	else

-	{

-		glBufferSubData(GL_ARRAY_BUFFER, 0, current_vertex_buffer_slot * sizeof(VertexBufferSlot), local_vertex_buffer);

-	}

-

-	if (++current_vertex_buffer >= TOTAL_VBOS)

-		current_vertex_buffer = 0;

-

 	glDrawArrays(GL_TRIANGLES, 0, 6 * current_vertex_buffer_slot);

 	current_vertex_buffer_slot = 0;

@@ -514,8 +492,11 @@

 		glBindVertexArray(vertex_array_id);

 	#endif

-		// Set up Vertex Buffer Objects

-		glGenBuffers(TOTAL_VBOS, vertex_buffer_ids);

+		// Set up Vertex Buffer Object

+		glGenBuffers(1, &vertex_buffer_id);

+		glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_id);

+		glVertexAttribPointer(ATTRIBUTE_INPUT_VERTEX_COORDINATES, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*)offsetof(Vertex, position));

+		glVertexAttribPointer(ATTRIBUTE_INPUT_TEXTURE_COORDINATES, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*)offsetof(Vertex, texture));

 		// Set up the vertex attributes

 		glEnableVertexAttribArray(ATTRIBUTE_INPUT_VERTEX_COORDINATES);

@@ -569,7 +550,7 @@

 		if (program_texture.id != 0)

 			glDeleteProgram(program_texture.id);

-		glDeleteBuffers(TOTAL_VBOS, vertex_buffer_ids);

+		glDeleteBuffers(1, &vertex_buffer_id);

 	#ifndef USE_OPENGLES2

 		glDeleteVertexArrays(1, &vertex_array_id);

 	#endif

@@ -590,7 +571,7 @@

 	glDeleteProgram(program_colour_fill.id);

 	glDeleteProgram(program_texture_colour_key.id);

 	glDeleteProgram(program_texture.id);

-	glDeleteBuffers(TOTAL_VBOS, vertex_buffer_ids);

+	glDeleteBuffers(1, &vertex_buffer_id);

 #ifndef USE_OPENGLES2

 	glDeleteVertexArrays(1, &vertex_array_id);

 #endif