您可以使用 glVertexAttribPointer 将较小的向量分配给较大的向量吗？
来自 OpenGL® ES 着色语言 (v1.00, r17) [PDF]（强调我的）：
赋值运算符将右值表达式的值存储到左值中，并返回具有左值表达式的类型和精度的右值。 左值表达式和右值表达式必须具有相同的类型。所有所需的类型转换都必须通过构造函数显式指定。
所以听起来这样做不是合法的：
vec3 my_vec3 = vec3(1, 2, 3);
vec4 my_vec4 = my_vec3;
并且为了使其合法，第二行必须是像：
vec4 my_vec4 = vec4(my_vec3, 1); // add 4th component
我假设 glVertexAttribPointer 有类似的要求。也就是说，如果您要分配给 vec4，则 size 参数必须等于 4。
然后我遇到了 适用于 Android 的 GLES20TriangleRenderer 示例。一些相关片段：
attribute vec4 aPosition;
maPositionHandle = GLES20.glGetAttribLocation(mProgram, "aPosition");
GLES20.glVertexAttribPointer(maPositionHandle, 3, GLES20.GL_FLOAT, false,
TRIANGLE_VERTICES_DATA_STRIDE_BYTES, mTriangleVertices);
所以 aPosition 是一个 vec4，但是对用于设置它的 glVertexAttribPointer 的调用具有 size > of 3. 此代码是否正确，GLES20TriangleRenderer 是否依赖于未指定的行为，或者是否还有其他我遗漏的内容？
From section 5.8 of The OpenGL® ES Shading Language (v1.00, r17) [PDF] (emphasis mine):
The assignment operator stores the value of the rvalue-expression into the l-value and returns an r-value with the type and precision of the lvalue-expression. The lvalue-expression and rvalue-expression must have the same type. All desired type-conversions must be specified explicitly via a constructor.
So it sounds like doing something like this would not be legal:
vec3 my_vec3 = vec3(1, 2, 3);
vec4 my_vec4 = my_vec3;
And to make it legal the second line would have to be something like:
vec4 my_vec4 = vec4(my_vec3, 1); // add 4th component
I assumed that glVertexAttribPointer had similar requirements. That is, if you were assigning to a vec4 that the size parameter would have to be equal to 4.
Then I came across the GLES20TriangleRenderer sample for Android. Some relevant snippets:
attribute vec4 aPosition;
maPositionHandle = GLES20.glGetAttribLocation(mProgram, "aPosition");
GLES20.glVertexAttribPointer(maPositionHandle, 3, GLES20.GL_FLOAT, false,
TRIANGLE_VERTICES_DATA_STRIDE_BYTES, mTriangleVertices);
So aPosition is a vec4, but the call to glVertexAttribPointer that's used to set it has a size of 3. Is this code correct, is GLES20TriangleRenderer relying on unspecified behavior, or is there something else I'm missing?
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传递给着色器的属性数据的大小不必与该着色器中属性的大小匹配。您可以将 2 个值（来自
glVertexAttribPointer）传递给定义为vec4的属性；剩下的两个值都为零，除了 W 分量为 1。同样，您可以将 4 个值传递给 vec2 属性；多余的值将被丢弃。因此，您可以根据需要将顶点属性与上传的值混合和匹配。
The size of the attribute data passed to the shader does not have to match the size of the attribute in that shader. You can pass 2 values (from
glVertexAttribPointer) to an attribute defined as avec4; the leftover two values are zero, except for the W component which is 1. And similarly, you can pass 4 values to avec2attribute; the extra values are discarded.So you can mix and match vertex attributes with uploaded values all you want.