shithub: cstory

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Use orphaning to slightly speed up rendering GPU-side

For some reason CPU usage is still double that of the SDLTexture
backend (SDL2 uses OpenGL 2.1, with glEnable/glDisable-style
immediate mode).

If I downgrade to OpenGL 2.1, and use VBO-less glDrawArrays, I get
great performance. I just wish I knew what the AMD driver is doing
that's so much faster.

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

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

@@ -255,7 +255,6 @@

 	// Set up Vertex Buffer Object

 	glGenBuffers(1, &vertex_buffer_id);

 	glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_id);

-	glBufferData(GL_ARRAY_BUFFER, sizeof(vertex_buffer), NULL, GL_STREAM_DRAW);

 	// Set up the vertex attributes

 	glEnableVertexAttribArray(1);

@@ -348,7 +347,7 @@

 	vertex_buffer.vertexes[3].x = -1.0f;

 	vertex_buffer.vertexes[3].y = 1.0f;

-	glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertex_buffer), &vertex_buffer);

+	glBufferData(GL_ARRAY_BUFFER, sizeof(vertex_buffer), &vertex_buffer, GL_STREAM_DRAW);

 	glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

 	SDL_GL_SwapWindow(window);

@@ -462,7 +461,7 @@

 	vertex_buffer.vertexes[3].x = vertex_left;

 	vertex_buffer.vertexes[3].y = vertex_bottom;

-	glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertex_buffer), &vertex_buffer);

+	glBufferData(GL_ARRAY_BUFFER, sizeof(vertex_buffer), &vertex_buffer, GL_STREAM_DRAW);

 	glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

 }

@@ -511,7 +510,7 @@

 	vertex_buffer.vertexes[3].x = vertex_left;

 	vertex_buffer.vertexes[3].y = vertex_bottom;

-	glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertex_buffer.vertexes), &vertex_buffer);

+	glBufferData(GL_ARRAY_BUFFER, sizeof(vertex_buffer), &vertex_buffer, GL_STREAM_DRAW);

 	glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

 }

@@ -641,7 +640,7 @@

 	vertex_buffer.vertexes[3].x = vertex_left;

 	vertex_buffer.vertexes[3].y = vertex_bottom;

-	glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertex_buffer), &vertex_buffer);

+	glBufferData(GL_ARRAY_BUFFER, sizeof(vertex_buffer), &vertex_buffer, GL_STREAM_DRAW);

 	if (glyph->pixel_mode == FONT_PIXEL_MODE_LCD)

 	{