android - OpenGL ES 2.0 : How to Implement Simultaneous Multi-Color gl_FragColor?

Question

我有一个 OpenGL ES Android 应用程序，我想找到一种方法让屏幕的多个部分同时以不同颜色发光。该应用程序本身将屏幕分为 6 列，当用户触摸该列时，该列会以独特的颜色亮起。

我遇到的问题是，当用户多次触摸屏幕时，所有列都会发出相同的颜色，而不是它们独特的颜色。原因是每次在列中检测到触摸时，我的渲染器逻辑都会覆盖 gl_FragColor。由于所有列都使用相同的着色器，因此在多点触摸情况下，所有列都以最近设置的颜色发光。

当用户一次触摸多个列时，我如何才能使每一列在触摸时都发出独特的颜色？由于 gl_FragColor 是一个自动生成的变量，我不确定如何添加更多 gl_FragColors，假设这有助于解决问题。

fragment 着色器

precision mediump float;         // Set the default precision to medium. We don't need as high of a
// precision in the fragment shader.
uniform sampler2D u_Texture;              // The input texture.

varying vec2 v_TexCoordinate;  // Interpolated texture coordinate per fragment.
varying vec3 v_Position;            // Interpolated position for this fragment.
varying vec4 v_Color;            // This is the color from the vertex shader interpolated across the triangle per fragment.
varying vec3 v_Normal;           // Interpolated normal for this fragment.

uniform vec4 ColumnGlowColor;          // color of the Column

uniform vec2 eColumnGlowPosition;   // where the Column is
uniform float eColumnGlowSizeScale; // the size to scale the glow
uniform vec2 aColumnGlowPosition;
uniform float aColumnGlowSizeScale;
uniform vec2 dColumnGlowPosition;
uniform float dColumnGlowSizeScale;
uniform vec2 gColumnGlowPosition;
uniform float gColumnGlowSizeScale;
uniform vec2 bColumnGlowPosition;
uniform float bColumnGlowSizeScale;
uniform vec2 eeColumnGlowPosition;
uniform float eeColumnGlowSizeScale;

float generateGlow( vec2 pixelPosition, float ColumnGlowScale, vec2 touchPosition){
if(stringGlowScale == 0.0) {
    return 0.0;
}
else if (touchPosition.y > pixelPosition.y){
    highp float distance = length(touchPosition-pixelPosition);  // the horizontal distance from the current pixel and the light source
    highp float threshold = .5*stringGlowScale;                             //defines the effect width
    highp float effectScale = sin((max(threshold-distance, .0))/threshold); // using sin function smooth the effect
    return effectScale;
}
else{
    highp float distance = abs(touchPosition.x-pixelPosition.x);  // the horizontal distance from the current pixel and the light source
    highp float threshold = .5*stringGlowScale;                             //defines the effect width
    highp float effectScale = sin((max(threshold-distance, .0))/threshold); // using sin function smooth the effect
    return effectScale;
}
}

// The entry point for our fragment shader.
void main(){
    highp float effectScale = 0.0;
    effectScale += generateGlow(v_Position.xy, eColumnGlowSizeScale, eColumnGlowPosition);
    effectScale += generateGlow(v_Position.xy, aColumnGlowSizeScale, aColumnGlowPosition);
    effectScale += generateGlow(v_Position.xy, dColumnGlowSizeScale, dColumnGlowPosition);
    effectScale += generateGlow(v_Position.xy, gColumnGlowSizeScale, gColumnGlowPosition);
    effectScale += generateGlow(v_Position.xy, bColumnGlowSizeScale, bColumnGlowPosition);
    effectScale += generateGlow(v_Position.xy, eeColumnGlowSizeScale, eeColumnGlowPosition);

    lowp vec4 fromTexture = texture2D(u_Texture, v_TexCoordinate);

    gl_FragColor = fromTexture + ColumnGlowColor*effectScale; 
}

渲染器

 public class OpenGL_GLRenderer implements GLSurfaceView.Renderer {
     ...

     private void setUniforms(int programHandle){
            ...
            mGlowColorHandle = GLES20.glGetUniformLocation(programHandle, "stringGlowColor");           //glow color
            mStringID = GLES20.glGetUniformLocation(programHandle, "stringNum");
            mGlowPosHandles[0] = GLES20.glGetUniformLocation(programHandle, "eStringGlowPosition");      //glow effect position on neck
            mGlowScaleHandles[0] = GLES20.glGetUniformLocation(programHandle, "eStringGlowSizeScale");   //glow effect strength
            mGlowPosHandles[1] = GLES20.glGetUniformLocation(programHandle, "aStringGlowPosition");
            mGlowScaleHandles[1] = GLES20.glGetUniformLocation(programHandle, "aStringGlowSizeScale");
            mGlowPosHandles[2] = GLES20.glGetUniformLocation(programHandle, "dStringGlowPosition");
            mGlowScaleHandles[2] = GLES20.glGetUniformLocation(programHandle, "dStringGlowSizeScale");
            mGlowPosHandles[3] = GLES20.glGetUniformLocation(programHandle, "gStringGlowPosition");
            mGlowScaleHandles[3] = GLES20.glGetUniformLocation(programHandle, "gStringGlowSizeScale");
            mGlowPosHandles[4] = GLES20.glGetUniformLocation(programHandle, "bStringGlowPosition");
            mGlowScaleHandles[4] = GLES20.glGetUniformLocation(programHandle, "bStringGlowSizeScale");
            mGlowPosHandles[5] = GLES20.glGetUniformLocation(programHandle, "eeStringGlowPosition");
            mGlowScaleHandles[5] = GLES20.glGetUniformLocation(programHandle, "eeStringGlowSizeScale");

            //************************Column Glow code*******************************
            //if user's touching the screen, make nearest string glow
            for (int i = 0; i< 6; i++) {
                if (stringGlowEffects[i] != null) {
                    float top = orthoTop + (orthoBottom-orthoTop)*stringGlowEffects[i].y + scroller.getCurrentValue();
                    GLES20.glUniform2f(mGlowPosHandles[i], stringGlowEffects[i].x, top);
                    float glowEffectScale = 1.0f + (50.0f) / 300.0f;
                    GLES20.glUniform1f(mGlowScaleHandles[i], glowEffectScale);      //TODO: allow multiple colors simultaneously
                    switch (i){
                        case 0:
                            GLES20.glUniform4f(mGlowColorHandle,.0f, .0f, 1.0f, 1.0f);
                            break;
                        case 1:
                            GLES20.glUniform4f(mGlowColorHandle,.0f, 1.0f, .0f, 1.0f);
                            break;
                        case 2:
                            GLES20.glUniform4f(mGlowColorHandle,1.0f, .0f, .0f, 1.0f);
                            break;
                        case 3:
                            GLES20.glUniform4f(mGlowColorHandle,.0f, 1.0f, 1.0f, 1.0f);
                            break;
                        case 4:
                            GLES20.glUniform4f(mGlowColorHandle,1.0f, 1.0f, .0f, 1.0f);
                            break;
                        case 5:
                            GLES20.glUniform4f(mGlowColorHandle,1.0f, .0f, 1.0f, 1.0f);
                            break;
                    }
                }
                else{
                    GLES20.glUniform1f(mGlowScaleHandles[i], 0.0f);
                }
            }
        }
    ...
 }

Answer 1

解决问题的最简单方法可能是为每个网格正方形设置颜色，而不是为颜色设置一个统一的颜色。您已经为列的位置和大小完成了此操作，您可以轻松地扩展它以记录每列的颜色。

在您的着色器中，您可以将 ColumnGlowColor 更改为一个数组(比拥有 6 个单独的变量更容易，就像您的位置和比例变量一样):

uniform vec4 ColumnGlowColor[6];          // color of the Column

如何实际将其应用到输出颜色很难说，因为您没有显示关于如何实际计算辉光的代码。假设 generateGlow 函数返回输入位置的辉光强度似乎是合理的。您可以让它返回一个 float4，而不是返回一个强度，它是颜色(在 RGB 分量中)和强度在 alpha 中。然后，您可以将像素着色器的最后一行更改为:

gl_FragColor = fromTexture + sumOfReturnsFromGenerateGlow; 

当您获得制服的位置时，您可能需要添加数组运算符以正确绑定(bind)它(一些驱动程序允许这样做，而另一些则不允许)。您的原始名称是 stringGlowColor，但它应该与统一名称相匹配:

mGlowColorHandle = GLES20.glGetUniformLocation(programHandle, "ColumnGlowColor[]");

当您设置mGlowColorHandle 值时，您将设置每个数组条目，方法是将索引添加到uniform。例如，对于第一列集将更改为:

GLES20.glUniform4f(mGlowColorHandle+i,.0f, .0f, 1.0f, 1.0f);

注意:如果使用 EXT_draw_buffers，您可以从着色器输出多种颜色。 GLES 扩展。但是，这不是您想要做的，因为我假设您没有多个帧缓冲区。