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DirectX 9: Switching from Fixed Function Pipeline to Shader Approach


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#1 xeon_rave   Members   -  Reputation: 141

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Posted 25 March 2014 - 08:31 AM

Hi guys,

 

I'm rolling my own rendering engine for 2d games. Before, I'm using Fixed Function Pipeline (FFP). I'm using dynamic vertex and index buffers. Lock/Unlock the buffers each frame. Batch the sprites(1 drawindexedprimitive() call for consecutive sprites that has the same texture).

 

Now, I would like to switch to Shader approach. As of now, I was able to draw a single rect using static vertex and index buffers, pass the computed World/View/Projection matrix to the shader (.fx file). It was great! I can now see my awesome rect with vertex colors. I'm no longer Locking/Unlocking my buffers every frame which I believe 1 of the slowest process. Anyway, my problem is how can I pass the vertices of each sprite + transformation matrix of each sprite to the shader? and how will this work on batching? like calling DrawIndexedPrimitive() one time for 10 sprites with same texture. As fas as I know based on what I learned, you can commit changes before calling the DrawIndexedPrimitive(). BUT how can you give all the information for those 10 sprites that will be drawn by this single DrawIndexedPrimitive call? OR it cant be done? Do you need 1 draw call for EACH sprite? I believe draw calls are slow too, right? if Yes, how can I pass the 4 vertices of each sprite to the shader? should i use:

 

uniform extern float3 vertex1;

uniform extern float3 vertex2;

uniform extern float3 vertex3;

uniform extern float3 vertex4;

 

then before draw calls, I use:

 

effect->SetFloat3(vertex1handle, &sprite.vertex1);

effect->SetFloat3(vertex2handle, &sprite.vertex2);

effect->SetFloat3(vertex3handle, &sprite.vertex3);

effect->SetFloat3(vertex4handle, &sprite.vertex4);

effect->CommitChanges();

draw(....);

 

 

BUT what if i need to draw a sprite with more than 4 vertices? like TRAILS (imagine the slash of Fruit Ninja).



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#2 Burnt_Fyr   Members   -  Reputation: 1249

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Posted 25 March 2014 - 09:23 AM

You likely want to look into instancing. Essentially you setup a buffer of world matrices for each sprite. These get bound to another stream, and your shader draws the sprite 1x for each matrix in the buffer, all in a single call.

 

http://msdn.microsoft.com/en-us/library/windows/desktop/bb173349%28v=vs.85%29.aspx



#3 SeanMiddleditch   Members   -  Reputation: 7257

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Posted 25 March 2014 - 02:18 PM

Now, I would like to switch to Shader approach. As of now, I was able to draw a single rect using static vertex and index buffers, pass the computed World/View/Projection matrix to the shader (.fx file). It was great! I can now see my awesome rect with vertex colors. I'm no longer Locking/Unlocking my buffers every frame which I believe 1 of the slowest process. Anyway, my problem is how can I pass the vertices of each sprite + transformation matrix of each sprite to the shader? and how will this work on batching? like calling DrawIndexedPrimitive() one time for 10 sprites with same texture. As fas as I know based on what I learned, you can commit changes before calling the DrawIndexedPrimitive(). BUT how can you give all the information for those 10 sprites that will be drawn by this single DrawIndexedPrimitive call? OR it cant be done? Do you need 1 draw call for EACH sprite? I believe draw calls are slow too, right? if Yes, how can I pass the 4 vertices of each sprite to the shader? should i use:


You pass the vertices the exact same way you did before.

You seem to be confused about how shaders work. There are multiple shader _stages_. Each stage works on a different piece of data. A vertex shader works on a single vertex, as its name implies. It doesn't care if you're drawing a point, a line, a triangle, or a whole mesh; it works on a single vertex at a time with no knowledge of or reason to care about the other vertices or even how many vertices there are.

The pixel/fragment shader runs on each fragment being drawn after rasterization. Again, it has no need to care about vertices. It doesn't matter whether a fragment is being rendered as part of a point, line, triangle, etc.; all it cares about is the single fragment it's drawing.

A geometry shader (and the tessellation shaders) _do_ care about the geomtric primitives being drawn. Simpler renderers don't use geometry shaders. To solve your issue of transforms, many just pre-transform the vertices of the sprite on the CPU before pushing them into a dynamic vertex buffer. Instancing would allow you to draw a single quad with a list of transforms, which requires only one draw call per shader/material (texture atlasing or texture arrays are essential here). A more advanced approach for 2D is to just draw a single instanced point for each sprite and to use the geometry shader to emit a quad (two triangles) for each input point; whether this is faster or not than the previous approach will depend on your target hardware, so try and profile both to be sure.

#4 cdoubleplusgood   Members   -  Reputation: 848

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Posted 26 March 2014 - 03:06 AM


A geometry shader (and the tessellation shaders) _do_ care about the geomtric primitives being drawn.

The topic is about D3D9, so geometry and tesselation shaders do not apply here.



#5 xeon_rave   Members   -  Reputation: 141

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Posted 27 March 2014 - 01:33 AM

Hmmm I think the "instancing" will solve my issue.

As I have read the link, the minimum shader version is 3.0. I would like to support more audience by at least moving to shader version 2.0.

Are there any other options rather than the instancing the shader 3.0 is using and rather than going back to Fixed Function Pipeline.

 

 

 


A geometry shader (and the tessellation shaders) _do_ care about the geomtric primitives being drawn.

The topic is about D3D9, so geometry and tesselation shaders do not apply here.

 

 

Why? DirectX9 doesn't support those kind of shaders?



#6 Phopojijo   Members   -  Reputation: 105

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Posted 30 March 2014 - 11:33 PM

Nope. Geometry Shaders were introduced in DirectX 10 and Tessellation in DirectX 11 (although proof of concepts exist for D3D10). Neither are available for DirectX 9.

 

Is there any particular reason for choosing DirectX 9?






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