DirectX9 C ++实时为顶点数据重新着色

Question

I'm very new to DirectX and I'm starting to get a grasp on how the API functions.

I've managed to get triangles showing and rendering properly using these functions:

Initializing the vertices:

void Menu::InitializeMenu(float x, float y, float width, float height, D3DCOLOR color,    IDirect3DDevice9* d3dDevice)
{
CUSTOMVERTEX vertices[] =
{
    { x, y, 0.5f, 1.0f, color },
    { x + width, y, 0.5f, 1.0f, color },
    { x + width, y + height, 0.5f, 1.0f, color },

    { x, y, 0.5f, 1.0f, color },
    { x , y + height, 0.5f, 1.0f, color },
    { x + width, y + height, 0.5f, 1.0f, color },
};

if (FAILED(d3dDevice->CreateVertexBuffer(6 * sizeof(CUSTOMVERTEX), 0, D3DFVF_CUSTOMVERTEX, D3DPOOL_DEFAULT, &m_vertexBuffer, NULL)))
    return;

void *locked_buffer;
if (FAILED(m_vertexBuffer->Lock(0, sizeof(vertices), (void **)&locked_buffer, 0)))
    return;



memcpy(locked_buffer, vertices, sizeof(vertices));
m_vertexBuffer->Unlock();
}

Everything here is defined within the Menu class.

Drawing:

void Menu::RenderMenu(IDirect3DDevice9 *d3dDevice)
{
d3dDevice->SetRenderState(D3DRS_LIGHTING, FALSE);
d3dDevice->SetRenderState(D3DRS_ALPHABLENDENABLE, TRUE);
d3dDevice->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_INVSRCALPHA);
d3dDevice->SetRenderState(D3DRS_SRCBLENDALPHA, D3DRS_DESTBLENDALPHA);
d3dDevice->SetStreamSource(0, m_vertexBuffer, 0, sizeof(CUSTOMVERTEX));
d3dDevice->SetFVF(D3DFVF_CUSTOMVERTEX);
d3dDevice->DrawPrimitive(D3DPT_TRIANGLELIST, 0, 2);
}

Everything works perfect, I get my two triangles rendered, which in turn produce a semi-transparent quad.

Now the Issue: I want to be able to change the colors of the vertices in my triangles after the program has started rendering (everything has been initialized already and rendered at least once).

Things I've thought about: -I've thought about calling the InitializeMenu function with different parameters to reinitialize the vertices with different color, reason I haven't done it is because it seems very inefficient and not practical.

-Materials: I have not implemented materials, this is because I don't know how (yet) and because I'm hoping to find a simpler alternative. All I need is the vertex colors. If materials are the only way to accomplish this, I will implement.

-Shaders: I understand you can color vertices with shaders, but I have very little shader experience, and as stated before I'd rather find a simpler alternative. Yes, I know shaders are simple, I've gotten to the point where I can change the color of vertices in a shader in real time. It was in GLSL but I'm sure it doesn't differ too much. Issue comes when I want to add multiple quads (collection of 2 triangles for ea quad). I only know how to change the color of all vertices coming into the vertex shader. As before though, if shaders is the only way to accomplish, I'll implement. Please just point me in the right direction. I have VERY little understanding on how shaders work on the low level (I understand the concept and flow, just don't know how to use to my advantage to use effectively).

-Research: I've looked everywhere, maybe I'm not asking my question properly, but I cannot find an answer anywhere.

This is actually my first time posting a question, usually someone has already asked my questions. I've tried to explain my problem as best as I could, but if it's still unclear feel free to ask for more code or information.

PS: I'm using windows 8 desktop, not sure if that really matters.

Answer 1

To update the vertices, you will need to do something similar to InitializeMenu, but without calling CreateVertexBuffer again. You will also need make a slight modification to how you create the vertex buffer.

There are two types of vertex buffers: static and dynamic. A static vertex buffer does not allow access by the CPU to make changes whereas a dynamic vertex buffer does.

To create a dynamic vertex buffer, add D3DUSAGE_DYNAMIC to CreateVertexBuffer:

d3dDevice->CreateVertexBuffer(6 * sizeof(CUSTOMVERTEX), D3DUSAGE_DYNAMIC, D3DFVF_CUSTOMVERTEX, D3DPOOL_DEFAULT, &m_vertexBuffer, NULL)

You can then make a new function like this to change color:

void Menu::ChangeColor(D3DColor color) {
    CUSTOMVERTEX *locked_buffer;
    if (FAILED(m_vertexBuffer->Lock(0, 0, (void **)&locked_buffer, 0))) {
        return;
    }

    for (int i=0; i<6; i++) {
        // use whatever you called color in your CUSTOMVERTEX struct
        locked_buffer[i].color = color;
    }
    m_vertexBuffer->Unlock();
}

This code essentially gets the vertex data from the GPU and allows you to update it on the CPU. You don't need to recreate the vertex buffer, you just update the values you want.

Answer 2

You can define a random function and then add color elements ie: Green, Blue, Yellow, Red, Purple etc into an array. Then you call the random function to randomly select the colors inside an array.

Like this:

int arr[15] = {10, 210, 140, 180, 250, 189, 183, 107, 183, 107, 60, 2, 55, 85, 48};

D3DCOLOR color1; D3DCOLOR color2; D3DCOLOR color3; D3DCOLOR color4;

srand(time(NULL));
CUSTOMVERTEX vertices[] =
{{ x, y, 0.5f, 1.0f, color = D3DCOLOR_XRGB(arr[rand() % 14 + 0], arr[rand() % 14 + 0], arr[rand() % 14 + 0])},
{ x + width, y, 0.5f, 1.0f, color = D3DCOLOR_XRGB(arr[rand() % 14 + 0], arr[rand() % 14 + 0], arr[rand() % 14 + 0])},
{ x + width, y + height, 0.5f, 1.0f, color = D3DCOLOR_XRGB(arr[rand() % 14 + 0], arr[rand() % 14 + 0], arr[rand() % 14 + 0])},

{ x, y, 0.5f, 1.0f, color = D3DCOLOR_XRGB(arr[rand() % 14 + 0], arr[rand() % 14 + 0], arr[rand() % 14 + 0])},
{ x , y + height, 0.5f, 1.0f, color = D3DCOLOR_XRGB(arr[rand() % 14 + 0], arr[rand() % 14 + 0], arr[rand() % 14 + 0])},
{ x + width, y + height, 0.5f, 1.0f, color = D3DCOLOR_XRGB(arr[rand() % 14 + 0], arr[rand() % 14 + 0], arr[rand() % 14 + 0])},
};

One thing, you might have to use different D3DCOLOR color variables ie; color1, color2, color3 etc to avoid dereferencing and value overwritting.