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glDrawArraysInstanced performance on Intel hd2000/3000

2 posts in this topic



I'm currently working on a game project which uses OpenTK targeting OpenGL 3.1.

After implementing instanced rendering ( instanced vertex attributes using glDrawArraysInstanced ) I've noticed a horrible performance drop on our intel test machine ( Intel HD3000 ).

It went from 2ms frame time to over 2000ms.

All other machines (using Amd and Nvidia cards) are performing better with instancing.

I've checked the intel site to make sure that the HD3000 supports OpenGL 3.1 and that it has the latest drivers.


Do you have any ideas what could be causing this issue?


Buffer Structures:

[StructLayout( LayoutKind.Sequential )]
struct VertexData
    public Vector3 Position;
    public Vector3 Normal;
    public Vector2 TexCoord;

    public static readonly int SizeInBytes = Marshal.SizeOf( new VertexData() );
    public VertexData( Vector3 position, Vector3 normal, Vector2 texcoord )
        Position = position;
        Normal = normal;
        TexCoord = texcoord;

[StructLayout( LayoutKind.Sequential )]
public struct InstanceData
    public Vector4 SpriteRect;
    public Vector4 DestinationRect;
    public Color4 Color;
    public Vector4 Scissors;

    public static readonly int SizeInBytes = Marshal.SizeOf( new InstanceData() );

VAO Creation:

float v1 = -1f;
float v2 = 1f;

VertexData[] Vertices = new VertexData[]
    new VertexData(
        new Vector3(v1, v2, 0),
        new Vector3(0, 0, 1),
        new Vector2(0, 0)),
    new VertexData(
        new Vector3(v2, v2, 0),
        new Vector3(0, 0, 1),
        new Vector2(1, 0)),
    new VertexData(
        new Vector3(v1, v1, 0),
        new Vector3(0, 0, 1),
        new Vector2(0, 1)),
    new VertexData(
        new Vector3(v1, v1, 0),
        new Vector3(0, 0, 1),
        new Vector2(0, 1)),
    new VertexData(
        new Vector3(v2, v2, 0),
        new Vector3(0, 0, 1),
        new Vector2(1, 0)),
    new VertexData(
        new Vector3(v2, v1, 0),
        new Vector3(0, 0, 1),
        new Vector2(1, 1))

Buffer vertexBuffer = Buffer.CreateVertexBuffer( Vertices, VertexData.SizeInBytes );
InstanceBuffer = Buffer.CreateInstanceBuffer( InstanceData.SizeInBytes, 4096 );

GL.GenVertexArrays( 1, out VAOHandle );
GL.BindVertexArray( VAOHandle );

// Vertex Buffer
GL.VertexAttribPointer( 0, 3, VertexAttribPointerType.Float, false, VertexData.SizeInBytes, 0 );
GL.EnableVertexAttribArray( 0 );

GL.VertexAttribPointer( 1, 3, VertexAttribPointerType.Float, false, VertexData.SizeInBytes, Vector3.SizeInBytes );
GL.EnableVertexAttribArray( 1 );

GL.VertexAttribPointer( 2, 2, VertexAttribPointerType.Float, false, VertexData.SizeInBytes, Vector3.SizeInBytes * 2 );
GL.EnableVertexAttribArray( 2 );

// Instance Buffer
GL.VertexAttribPointer( 3, 4, VertexAttribPointerType.Float, false, InstanceData.SizeInBytes, 0 );
GL.EnableVertexAttribArray( 3 );
GL.VertexAttribDivisor( 3, 1 );

GL.VertexAttribPointer( 4, 4, VertexAttribPointerType.Float, false, InstanceData.SizeInBytes, Vector4.SizeInBytes );
GL.EnableVertexAttribArray( 4 );
GL.VertexAttribDivisor( 4, 1 );

GL.VertexAttribPointer( 5, 4, VertexAttribPointerType.Float, false, InstanceData.SizeInBytes, Vector4.SizeInBytes * 2 );
GL.EnableVertexAttribArray( 5 );
GL.VertexAttribDivisor( 5, 1 );

GL.VertexAttribPointer( 6, 4, VertexAttribPointerType.Float, false, InstanceData.SizeInBytes, Vector4.SizeInBytes * 3 );
GL.EnableVertexAttribArray( 6 );
GL.VertexAttribDivisor( 6, 1 );

GL.BindVertexArray( 0 );

Vertex Shader:

#version 140

// Vertex Data
in vec3 in_position;
in vec3 in_normal;
in vec2 in_texcoord;
// Instance Data
in vec4 in_spriteRect;
in vec4 in_destinationRect;
in vec4 in_color;
in vec4 in_scissors;

// Output
out vec3 vs_normal;
out vec2 vs_texcoord;
out vec4 vs_color;
out vec4 vs_scissors;

void main()
	// Texture Coordinates
	vs_texcoord = in_texcoord;
	vs_texcoord *= in_spriteRect.zw;
	vs_texcoord += in_spriteRect.xy;

	// Position
	vec4 Position = vec4( in_position, 1.0f );

	// Normalize to [0, 1]
	Position.xy = Position.xy * 0.5f + 0.5f;

	// Apply Destination Transform
	Position.xy *= in_destinationRect.zw;
	Position.xy += in_destinationRect.xy;

	// Normalize to [-1, 1]
	Position.xy = Position.xy * 2.0f - 1.0f;

	// In OpenGL -1,-1 is the bottom left screen corner
	// In DirectX -1,-1 is the top left screen corner
	Position.y += 2.0f - in_destinationRect.w * 2.0f;

	vs_normal = in_normal;
	vs_color = in_color;
	vs_scissors = in_scissors;

	gl_Position = Position;

Fragment Shader:

#version 140

uniform sampler2D Tex;

// Input
in vec3 vs_normal;
in vec2 vs_texcoord;
in vec4 vs_color;
in vec4 vs_scissors;

// Output
out vec4 out_frag_color;

bool ScissorTest()
	return	gl_FragCoord.x > vs_scissors.x &&
			gl_FragCoord.y > vs_scissors.y &&
			gl_FragCoord.x < vs_scissors.x + vs_scissors.z &&
			gl_FragCoord.y < vs_scissors.y + vs_scissors.w;

void main()
	out_frag_color = vec4(0, 0, 0, 0);

			out_frag_color = texture( Tex, vs_texcoord ) * vs_color;


InstanceBuffer.Write( InstanceDataCPU, InstanceData.SizeInBytes, InstanceCount );
GL.BindVertexArray( VAOHandle );
BindTexture( TextureHandle, 0, texture );
GL.UseProgram( ProgramHandle );
GL.DrawArraysInstanced( PrimitiveType.Triangles, 0, 6, InstanceCount );

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Intel does support GL.DrawArraysInstanced, so it appears that you are hitting a slow path or falling back to software emulation for some reason.


I would suggest using Intel's Graphics Performance Analyzer to understand what is happening and why. If the drivers support ARB_debug_output, you could also use that to get more insight on potential issues.


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Thanks for the suggestions!


Unfortunately the hd3000 does not support ARB_debug_output,

and afaik Intel's Graphics Performance Analyzer doesn't support OpenGL on Windows yet.


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