objective-c - 为什么我在 OpenGL ES for iOS 中使用 GL_UNSIGNED_SHORT 时得到 EXC_BAD_ACCESS？

Question

我需要做的是绘制一个包含超过 256 个元素的顶点数组。当我的数量少于那么多时，并且在调用 glDrawElements 时使用 GL_UNSIGNED_BYTE，一切正常。当我有超过 256 个元素时，它会再次从第一个顶点开始绘制(即，最后一个元素 [256 - 255，无论什么] 与第一个 [1 或 0] 连接，并且不会绘制更多元素)。如果我改用 GL_UNSIGNED_SHORT，我会得到 EXC_BAD_ACCESS。给了什么？

int indexLim = self.animIndex;

GLushort glIndLim = (GLushort)indexLim;

Vertex localVertices[glIndLim];
GLubyte localIndices[glIndLim];

for(GLushort i=0; i < glIndLim; i++)
{
    x = (float)i;
    y = [[data objectAtIndex:i ] floatValue];

    x = x*xScale + xOffset;
    y = y*yScale + yOffset;

    localVertices[i].Position[0] = x;
    localVertices[i].Position[1] = y;
    localVertices[i].Position[2] = z;
    localVertices[i].Color[0]    = r;
    localVertices[i].Color[1]    = g;
    localVertices[i].Color[2]    = b;
    localVertices[i].Color[3]    = a;
    localIndices[i] = i;
}    

// setupVBOs
GLuint vertexBuffer;
glGenBuffers(1, &vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(localVertices), localVertices, GL_STATIC_DRAW);

GLuint indexBuffer;
glGenBuffers(1, &indexBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(localIndices), localIndices, GL_STATIC_DRAW);

glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), 0);
glVertexAttribPointer(_colorSlot, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*) (sizeof(float) * 3));


//glDrawElements(GL_LINE_STRIP, glIndLim, GL_UNSIGNED_BYTE, 0); // Works, but only draws 256 elements
glDrawElements(GL_LINE_STRIP, glIndLim, GL_UNSIGNED_SHORT, 0); // EXC_BAD_ACCESS!!!!

Answer 1

你试过定义:

GLubyte localIndices[glIndLim];

作为

GLushort localIndices[glIndLim];

?

原因是，如果它应该代表您的顶点的索引，它应该接受 GLushort 的所有可能值，否则本地索引将始终是 GLubyte。