Sign in to follow this  

Material alpha blending in managed DirectX

This topic is 3453 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

I have the following code:
using System;
using System.Drawing;
using System.Windows.Forms;
using Microsoft.DirectX;
using Microsoft.DirectX.Direct3D;

namespace TestProgram {
    class TestForm : Form {
        Mesh mesh1;
        Mesh mesh2;
        Device device;

        public TestForm() {
            PresentParameters present;
            present = new PresentParameters();
            present.Windowed = true;
            present.AutoDepthStencilFormat = DepthFormat.D16;
            present.EnableAutoDepthStencil = true;
            present.SwapEffect = SwapEffect.Discard;
            present.MultiSample = MultiSampleType.TwoSamples;
            present.BackBufferWidth = 1280;
            present.BackBufferHeight = 1024;
            present.BackBufferFormat = Format.R5G6B5;

            device = new Device(0, DeviceType.Hardware, this,
                                CreateFlags.HardwareVertexProcessing, present);
            device.DeviceReset += new EventHandler(OnDeviceReset);
            OnDeviceReset(null, EventArgs.Empty);

            mesh1 = Mesh.Box(device, 100.0f, 100.0f, 100.0f);
            mesh2 = Mesh.Box(device, 50.0f, 50.0f, 50.0f);

        private void OnDeviceReset(object sender, EventArgs e) {

            device.Transform.Projection = Matrix.PerspectiveFovRH(
               (float)Math.PI / 4.0F,
               (float)this.ClientSize.Width / (float)this.ClientSize.Height,
               0.001f, 1000);

            device.Transform.View = Matrix.LookAtRH(new Vector3(90, 0, 300),
                new Vector3(0, 0, 0), new Vector3(0, 1, 0));

            device.RenderState.Lighting = true;

            device.Lights[0].Diffuse = Color.White;
            device.Lights[0].Specular = Color.White;
            device.Lights[0].Type = LightType.Directional;
            device.Lights[0].Direction = new Vector3(-19, -5, -40);
            device.Lights[0].Enabled = true;
            device.Lights[0].Attenuation0 = 1000.0f;
            device.RenderState.CullMode = Cull.None;
            device.RenderState.Ambient = System.Drawing.Color.White;

        protected override void OnPaint(PaintEventArgs e) {
            Material material = new Material();

            device.Clear(ClearFlags.Target | ClearFlags.ZBuffer,
                        Color.White, 1.0f, 0);

            material.Ambient = Color.FromArgb(255, 0, 0, 255);
            material.Diffuse = Color.FromArgb(255, 0, 0, 255);
            material.Emissive = Color.FromArgb(255, 0, 0, 255);
            material.Specular = Color.FromArgb(255, 0, 0, 255);
            device.RenderState.AlphaBlendEnable = false;
            device.Material = material;

            material.Ambient = Color.FromArgb(30, 255, 0, 0);
            material.Diffuse = Color.FromArgb(30, 255, 0, 0);
            material.Emissive = Color.FromArgb(30, 255, 0, 0);
            material.Specular = Color.FromArgb(30, 255, 0, 0);
            device.RenderState.AlphaBlendEnable = true;
            device.RenderState.DiffuseMaterialSource = ColorSource.Material;
            device.Material = material;


        static void Main() {
            Application.Run(new TestForm());

It must draw transparent red cube and blue cube seen through it. But I have a following picture: Where I mistaken?

Share this post

Link to post
Share on other sites
For one thing, you first draw a solid red cube. Once that's drawn, nothing inside that cube will be rendered.

It sounds like you should render the inside cube first, with alpha=1. Then render the red cube with alpha < 1.

Share this post

Link to post
Share on other sites
Noup, first I draw blue cube, which is smaller when red cube and placed inside it.

Share this post

Link to post
Share on other sites
After enabling alpha blending you must choose how to blend.

What you're doing is done via:

This says to multiply the new (src) pixels by the new alpha,
Multiply the old (dest) pixels by (1-new alpha)
Add the results

color = newcolor*newalpha + oldcolor*(1-newalpha);

You may also need to adjust the texture stages to use vertex/material alpha. I'll show using color without texture here)

pDev->SetTextureStageState(0, D3DTSS_COLOROP, D3DTOP_SELECTARG1);
pDev->SetTextureStageState(0, D3DTSS_COLORARG1, D3DTA_DIFFUSE);
pDev->SetTextureStageState(0, D3DTSS_ALPHAOP, D3DTOP_SELECTARG1);
pDev->SetTextureStageState(0, D3DTSS_ALPHAARG1, D3DTA_DIFFUSE);

pDev->SetTextureStageState(1, D3DTSS_COLOROP, D3DTOP_DISABLE);
pDev->SetTextureStageState(1, D3DTSS_ALPHAOP, D3DTOP_DISABLE);

This sets up a simple single stage which just takes the diffuse color and outputs to the blending stage.

Share this post

Link to post
Share on other sites
Sign in to follow this