Drawing Multiple 2d shapes in DirectX

Question

I completed a tutorial on rendering 2d triangles in directx. Now, I want to use my knowledge of rendering a single triangle to render multiple triangles, or for that matter multiple objects on screen.

Should I create a list/stack/vector of vertexbuffers and input layouts and then draw each object? Or is there a better approach to this?

My process would be:

• Setup directx, including vertex and pixel shaders
• Create vertex buffers for each shape that has to be drawn on the screen and store them in an array.
• Draw them to the render target for each frame(each frame)
• Present the render target(each frame)

Please assume very rudimentary knowledge of DirectX and graphics programming in general when answering.

Answer 1

You don't need to create vertex buffer for each shape, you can just create one to store all the vertices of all triangles, then create a index buffer to store all indices of all shapes, at last draw them with index buffer. I am not familiar with DX11, So, I just list the links for D3D 9 for your reference, I think the concept was same, just with some API changes.

Index Buffers(Direct3D 9)

Rendering from Vertex and Index buffers

If the triangles are in the same shape, just with different position or colors, you can consider using geometry instancing, it's a powerful way to render multiple copies of the same geometry.

Geometry Instancing

Efficiently Drawing Multiple Instances of Geometry(D3D9)

Answer 2

I don't know much about DirectX but general rule in rendering on GPU is to use separate vertex and index buffers for every mesh.

Although there is nothing limiting you from using single vertex buffer with many index buffers, in fact you may get some performance gains especially for small meshes...

Answer 3

You'll need just one vertex buffer for do this , and then Batching them,

so here is what you can do, you can make an array/vector holding the triangle information, let's say (pseudo-code)

struct TriangleInfo{
  ..... texture;
  vect2 pos;
  vect2 dimension;
  float rot;

}

then in you draw method

for(int i=0; i < vector.size(); i++){

    TriangleInfo tInfo = vector[i];
    matrix worldMatrix = Transpose(matrix(tInfo.dimension) * matrix(tInfo.rot) * matrix(tInfo.pos));

    shaderParameters.worldMatrix = worldMatrix; //info to the constabuffer

    ..
    ..
    dctx->PSSetShaderResources(0, 1, &tInfo.texture);
    dctx->Draw(0,4);
}

then in your vertex shader:

cbuffer cbParameters : register( b0 ) { 
    float4x4 worldMatrix; 
};

VOut main(float4 position : POSITION, float4 texCoord : TEXCOORD)
{
    ....
    output.position = mul(position,worldMatrix);
    ...

}

Remenber all is pseudo-code, but this should give you the idea, but there is a problem if you are planing to make a lot of Triangle, let's say 1000 triangles, maybe this is not the best option, you should using DrawIndexed and modifying the vertex position of each triangle, or you can use DrawInstanced , that is simpler , to be able to send all the information in just once Draw call, because calling Draw * triangleCount , is very heavy for large amounts