Question

我正在尝试使用Qt的OpenGL类渲染场景（下面显示的平台上的自行车）。

Screenshot of bike model without shadows

我意识到我们需要为此做两次传递。

从灯光的角度渲染深度贴图的第一道过程第二个用于从相机的角度渲染场景片段着色器使用深度贴图作为确定是否的纹理碎片是否在阴影内。

为了捕捉深度图，我正在从灯光渲染场景进入帧缓冲区的观点如下

uint ShadowRenderWindow::renderToShadowMap()
{
    if(!m_shadowFBO)
    {
        m_shadowFBO = new QOpenGLFramebufferObject(1024,
1024, QOpenGLFramebufferObject::Depth);
        m_shadowFBO->bind();
        glDrawBuffer(GL_NONE);
        glReadBuffer(GL_NONE);
        m_shadowFBO->release();
    }

    m_shadowFBO->bind();

    glViewport(0, 0, m_shadowFBO->width(), m_shadowFBO->height());
    glEnable(GL_DEPTH_TEST);
    glClear(GL_DEPTH_BUFFER_BIT);

    m_lightViewMatrix.setToIdentity();
    m_lightViewMatrix.lookAt(
      m_lightPositionMatrix.map( QVector3D(0,0,0) ),
      m_sceneBounds.center(),
      m_lightPositionMatrix.map( QVector3D(0,1,0) ).normalized() );

    for(int i=0; i<m_models.size()-1; i++)
    {
        ObjModel *model = m_models.at(i);
        model->setRenderMode(ObjModel::ShadowMode);
        model->render(m_projectionMatrix, m_lightViewMatrix);
    }

    m_shadowFBO->release();

    return m_shadowFBO->texture();
}

使用

渲染每个模型

m_shader->bind();
model->m_vertexBuffer->bind();
model->m_indexBuffer->bind();

const QMatrix4x4 lightViewProjectionMatrix = projectionMatrix *
lightViewMatrix * model->m_matrix;

m_shader->enableAttributeArray("qt_Vertex");
m_shader->setAttributeBuffer("qt_Vertex", GL_FLOAT, 0, 3, 0);

m_shader->setUniformValue("qt_LightViewProjectionMatrix",
lightViewProjectionMatrix);

Q_FOREACH(ObjModel::Part part, model->m_parts)
{
    const uint offset = part.start * sizeof(uint);
    glDrawElements(part.type, part.length,
         GL_UNSIGNED_INT, (void*)offset);
}

model->m_indexBuffer->release();
model->m_vertexBuffer->release();
m_shader->release();

带顶点着色器

attribute vec3 qt_Vertex;
uniform mat4 qt_LightViewProjectionMatrix;
const float c_one = 1.0;

void main(void)
{
    gl_Position = qt_LightViewProjectionMatrix * vec4(qt_Vertex, c_one);
}

和片段着色器

void main(void)
{
    gl_FragDepth = gl_FragCoord.z;
}

然后在第二遍中使用阴影纹理，我这样做第二遍的片段着色器。

float evaluateShadow(in vec4 shadowPos)
{
    vec3 shadowCoords = shadowPos.xyz / shadowPos.w;
    shadowCoords = shadowCoords * 0.5 + 0.5;

    float closestDepth = texture2D(qt_ShadowMap, shadowCoords.xy).r;
    float currentDepth = shadowPos.z;
    float shadow = (currentDepth > closestDepth) ? 1.0 : 0.5;

    return shadow;
}

void main(void)
{
    vec4 lmColor = evaluateLightMaterialColor(v_Normal);
    if(qt_ShadowEnabled == true)
    {
        float shadow = evaluateShadow(v_ShadowPosition);
        gl_FragColor = vec4(lmColor.xyz * shadow, qt_Material.opacity);
    }
    else
        gl_FragColor = lmColor;
}

但上述所有内容似乎没有任何区别。我无法看到任何第二遍中的影子。

有人可以指点我出错的地方吗？

Answer 1

由于使用QOpenGLFrameBufferObject是不可能的，我必须使用gl函数调用自己创建缓冲区，如下所示。

// Refer http://learnopengl.com/#!Advanced-Lighting/Shadows/Shadow-Mapping
if(m_shadowMapFBO != 0)
    return;

// Create a texture for storing the depth map
glGenTextures(1, &m_shadowMapTex);
glBindTexture(GL_TEXTURE_2D, m_shadowMapTex);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT,
             SHADOW_WIDTH, SHADOW_HEIGHT, 0, GL_DEPTH_COMPONENT, GL_FLOAT, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
GLfloat borderColor[] = { 1.0, 1.0, 1.0, 1.0 };
glTexParameterfv(GL_TEXTURE_2D, GL_TEXTURE_BORDER_COLOR, borderColor);

// Create a frame-buffer and associate the texture with it.
glGenFramebuffers(1, &m_shadowMapFBO);
glBindFramebuffer(GL_FRAMEBUFFER, m_shadowMapFBO);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, m_shadowMapTex, 0);

// Let OpenGL know that we are not interested in colors for this buffer
glDrawBuffer(GL_NONE);
glReadBuffer(GL_NONE);

// Cleanup for now.
glBindFramebuffer(GL_FRAMEBUFFER, 0);
glBindTexture(GL_TEXTURE_2D, 0);

然后我通过绑定阴影纹理来渲染场景。片段着色器代码必须稍微更新一下，以确定片段是位于阴影内还是位于阴影内。

const float qt_ZNear=0.1;
const float qt_ZFar=1000.0;

float linearizeDepth(float depth)
{
    float z = depth * 2.0 - 1.0; // Back to NDC
    return (2.0 * qt_ZNear * qt_ZFar) / (qt_ZFar + qt_ZNear - z * (qt_ZFar - qt_ZNear));
}
float evaluateShadow(in vec4 shadowPos)
{
    vec3 shadowCoords = shadowPos.xyz / shadowPos.w;
    shadowCoords = shadowCoords * c_half + c_half;

    if(shadowCoords.z > c_one)
        return c_one;

    float closestDepth = linearizeDepth( texture2D(qt_ShadowMap, shadowCoords.xy).r );
    float currentDepth = shadowPos.z;
    float shadow = (currentDepth < closestDepth) ? c_one : c_half;

    return shadow;
}

With that done, I was now able to render the bike with shadows

The complete code can be downloaded from here

Answer 2

编辑：显然现在还不能将QOpenGLFrameBufferObject用于此用例（http://lists.qt-project.org/pipermail/interest/2016-February/020786.html）

如何使用QOpenGLFrameBufferObject进行阴影贴图？

2 个答案: